THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 


PRESENTED  BY 

PROF.  CHARLES  A.  KOFOID  AND 
MRS.  PRUDENCE  W.  KOFOID 


VARIOUS  KINDS  OF  BACTERIA. 

A.  To  the  left  the  common  hay  bacillus  {Bacillus  subtilis)  \  to  the  right  a  Spiril- 
lum. B.  A  Coccus  form  (Planococcus).  C,  D,  E.  Species  of  Pseudomonas. 
F,  G.  Species  of  Bacillus \  F  being  that  of  typhoid  fever.  H.  Microspira. 
/,  K,  L,  M.  Species  of  Spirillum.— (After  Engler  and  Prantl.) 


THE  STORY  OF 
GERM   LIFE 


BY 

H.   W.   CONN 


PROFESSOR   OF   BIOLOGY   AT   WESLEYAN    UNIVERSITY, 

AUTHOR   OF   EVOLUTION    OF   TO-DAY, 

THE   LIVING   WORLD,   ETC. 


WITH  ILLUSTRA  TIONS 


NEW    YORK 

D.    APPLETON    AND    COMPANY 
1904 


COPYRIGHT,  1897, 
BY  D.  APPLETON  AND  COMPANY. 


PREFACE. 


THE  rapid  progress  of  discovery  in  the  last 
few  years  has  created  a  very  general  interest  in 
bacteria.  Few  people  who  read  could  be  found 
to-day  who  have  not  some  little  idea  of  these 
organisms  and  their  relation  to  disease.  It  is, 
however,  unfortunately  a  fact  that  it  is  only  their 
relation  to  disease  which  has  been  impressed  upon 
the  public.  The  very  word  bacteria,  or  microbe, 
conveys  to  most  people  an  idea  of  evil.  The  last 
few  years  have  above  all  things  emphasized  the 
importance  of  these  organisms  in  many  relations 
entirely  independent  of  disease,  but  this  side  of 
the  subject  has  not  yet  attracted  very  general 
attention,  nor  does  it  yet  appeal  to  the  reader 
with  any  special  force.  It  is  the  purpose  of  the 
following  pages  to  give  a  brief  outline  of  our 
knowledge  of  bacteria  and  their  importance  in 
the  world,  including  not  only  their  well-known 
agency  in  causing  disease,  but  their  even  greater 
importance  as  agents  in  other  natural  phenomena. 
It  is  hoped  that  the  result  may  be  to  show  that 
these  organisms  are  to  be  regarded  not  primarily 
in  the  light  of  enemies,  but  as  friends,  and  thus 
to  correct  some  of  the  very  general  but  erroneous 
ideas  concerning  their  relation  to  our  life. 

MIDDLETOWN,  April  /,  /<?97. 
3 


M336376 


CONTENTS. 


CHAPTER  PAGE 

I. — BACTERIA  AS  PLANTS      .       .       .  .       .9 

Historical. — Form  of  bacteria. — Multiplication  of  bac- 
teria.— Spore  formation. — Motion. — Internal  structure. — 
Animals  or  plants  ? — Classification. — Variation.  —Where 
bacteria  are  found. 

II. — MISCELLANEOUS  USES  "OF  BACTERIA  IN  THE  ARTS.   41 

Maceration  industries.  —  Linen.  —  Jute.  —  Hemp.  — 
Sponges.  —  Leather.  —  Fermentative  industries. — Vine- 
gar.— Lactic  acid. — Butyric  acid. — Bacteria  in  tobacco 
curing.  — Troublesome  fermentations. 

III.— BACTERIA  IN  THE  DAIRY       .     •>:'••        •        •   66 

Sources  of  bacteria  in  milk. — Effect  of  bacteria  on 
milk. —Bacteria  used  in  butter  making. — Bacteria  in 
cheese  making. 

IV. — BACTERIA  IN  NATURAL  PROCESSES        .       .        .94 

Bacteria  as  scavengers. — Bacteria  as  agents  in  Nature's 
food  cycle. — Relation  of  bacteria  to  agriculture. — Sprout- 
ing of  seeds. — -The  silo. — The  fertility  of  the  soil. — Bac- 
teria as  sources  of  trouble  to  the  farmer. — Coal  forma- 
tion. 

V. — PARASITIC  BACTERIA  AND   THEIR  RELATION  TO 

DISEASE      .      "  .        ,        .        ,        .        .        .128 

Method  of  producing  disease. — Pathogenic  germs  not 
strictly  parasitic. — Pathogenic  germs  that  are  true  para- 
sites. —What  diseases  are  due  to  bacteria. — Variability 


6  THE  STORY  OF  GERM   LIFE. 

CHAPTER  PAGE 

of  pathogenic  powers. — Susceptibility  of  the  individual. 
—  Recovery  from  bacteriological  diseases.  —  Diseases 
caused  by  organisms  other  than  bacteria. 

VI. — METHODS  OF  COMBATING  PARASITIC  BACTERIA    .  165 

Preventive  medicine. — Bacteria  in  surgery. — Preven- 
tion by  inoculation.— Limits  of  preventive  medicine. — 
Curative  medicine. — Drugs. — Vis  medicatrix  naturae. — 
Antitoxines  and  their  use. — Conclusion. 


LIST  OF  ILLUSTRATIONS. 


FIGURE  PAGE 

Various  kinds  of  bacteria  .        .        .      Frontispiece 

1.  General  shapes  of  bacteria        .        *        .        .        .  18 

2.  Method  of  multiplication  of  bacteria  ig 

3.  Micrococci         .                 .        .         .         .        .         .  ig 

4.  Streptococci       .        .        .        •        »        «        .        .  ig 

5.  Sarcina       .        . 20 

6.  Separate  rods  showing  variations  in  size    ...  20 

7.  Rod-forms  united  to  form  chains       ....  20 

8.  Various  types  of  spiral  bacteria 21 

g.  Various  shaped  rods 23 

10.  Bacteria  surrounded  by  capsules        ....  23 

11.  Various  types  of  bacteria  "colonies"         •        .        .24 

12.  Endogenous  spores    .......  26 

13.  So-called  arthrogenous  spores    .         .         .         .         .  27 

14.  Formation  of  spores  in  unusual  forms  (Crenothrix)   .  28 

15.  Bacteria  provided  with  flagella .         «        .         .         .  2g 

16.  Internal  structure  of  bacteria    .....  30 

17.  Threads  of  Oscillaria         .        .         .         .         .         .  32 

1 8.  Bacillus  aceticum,  of  vinegar 53 

ig.  Bacillus  acidi  lactici,  of  sour  milk      .         .         .  71 

20.  Dairy  bacterium  producing  red  milk ....  73 

21.  Dairy  bacterium  producing  pleasant  flavours  in  butter  80 

22.  Dairy  bacterium  producing  pleasant  aroma  in  butter  81 

23.  Dairy  bacterium  producing  pleasant  flavour  in  butter  83 

24.  Dairy  bacterium  producing  "  swelled  "  cheese  .         .  g2 

25.  Diagram  illustrating  Nature's  food  cycle  .         .        .  gg 

7 


8  LIST  OF  ILLUSTRATIONS. 

FIGURE  PAGE 

26.  Soil  bacteria  which  produce  nitrification   .        .        .     103 

27.  Soil  bacteria  which  produce  tubercles  on  the  roots  of 

legumes 108 

28.  Diphtheria  bacillus 134 

29.  Tetanus  bacillus      .  .»        .        .        v       .       '••        .  135 

30.  Typhoid  bacillus 136 

31.  Tuberculosis  bacillus       •  ,,  • 137 

32.  Anthrax  bacillus         .     •   .        .         .        .        .        .  138 

33.  White  blood  corpuscles  and  other  phagocytes  .        .152 

34.  Malarial  organism 161 


THE  STORY   OF  GERM   LIFE. 


CHAPTER   I. 

BACTERIA    AS    PLANTS. 

DURING  the  last  fifteen  years  the  subject  of 
bacteriology*  has  developed  with  a  marvellous 
rapidity.  At  the  beginning  of  the  ninth  decade 
of  the  century  bacteria  were  scarcely  heard  of 
outside  of  scientific  circles,  and  very  little  was 
known  about  them  even  among  scientists.  To- 
day they  are  almost  household  words,  and  every- 
one who  reads  is  beginning  to  recognise  that 
they  have  important  relations  to  his  everyday 
life.  The  organisms  called  bacteria  comprise 
simply  a  small  class  of  low  plants,  but  this  small 
group  has  proved  to  be  of  such  vast  importance 
in  its  relation  to  the  world  in  general  that  its 
study  has  little  by  little  crystallized  into  a  science 
by  itself.  It  is  a  somewhat  anomalous  fact  that 
a  special  branch  of  science,  interesting  such  a 
large  number  of  people,  should  be  developed 
around  a  small  group  of  low  plants.  The  impor- 
tance of  bacteriology  is  not  due  to  any  importance 
bacteria  have  as  plants  or  as  members  of  the 
vegetable  kingdom,  but  solely  to  their  powers  of 

*  The  term  microbe  is   simply  a  word  which  has  been 
coined  to  include  all  of  the  microscopic  plants  commonly  in- 
cluded under  the  terms  bacteria  and  yeasts. 
9 


10  THE  STORY  OF  GERM   LIFE. 

producing  profound  changes  in  Nature.  There  is 
no  one  family  of  plants  that  begins  to  compare 
with  them  in  importance.  It  is  the  object  of  this 
work  to  point  out  briefly  how  much  both  of  good 
and  ill  we  owe  to  the  life  and  growth  of  these 
microscopic  organisms.  As  we  have  learned 
more  and  more  of  them  during  the  last  fifty  years, 
it  has  become  more  and  more  evident  that  this 
one  little  class  of  microscopic  plants  fills  a  place 
in  Nature's  processes  which  in  some  respects  bal- 
ances that  filled  by  the  whole  of  the  green  plants. 
Minute  as  they  are,  their  importance  can  hardly 
be  overrated,  for  upon  their  activities  is  founded 
the  continued  life  of  the  animal  and  vegetable 
kingdom.  For  good  and  for  ill  they  are  agents 
of  neverceasing  and  almost  unlimited  powers. 

HISTORICAL. 

The  study  of  bacteria  practically  began  with 
the  use  of  the  microscope.  It  was  toward  the 
close  of  the  seventeenth  century  that  the  Dutch 
microscopist,  Leeuwenhoek,  working  with  his  sim- 
ple lenses,  first  saw  the  organisms  which  we  now 
know  under  this  name,  with  sufficient  clearness 
to  describe  them.  Beyond  mentioning  their  ex- 
istence, however,  his  observations  told  little  or 
nothing.  Nor  can  much  more  be  said  of  the  stud- 
ies which  followed  during  the  next  one  hundred 
and  fifty  years.  During  this  long  period  many  a 
microscope  was  turned  to  the  observation  of  these 
minute  organisms,  but  the  majority  of  observers 
were  contented  with  simply  seeing  them,  marvel- 
ling at  their  minuteness,  and  uttering  many  excla- 
mations of  astonishment  at  *he  wonders  of  Nature. 
A  few  men  of  more  strictly  scientific  natures  paid 


BACTERIA  AS  PLANTS.  11 

some  attention  to  these  little  organisms.  Among 
them  we  should  perhaps  mention  Von  Gleichen, 
Muller,  Spallanzani,  and  Needham.  Each  of 
these,  as  well  as  others,  made  some  contributions 
to  our  knowledge  of  microscopical  life,  and  among 
other  organisms  studied  those  which  we  now  call 
bacteria.  Speculations  were  even  made  at  these 
early  dates  of  the  possible  causal  connection  of 
these  organisms  with  diseases,  and  for  a  little  the 
medical  profession  was  interested  in  the  sugges- 
tion. It  was  impossible  then,  however,  to  obtain 
any  evidence  for  the  truth  of  this  speculation,  and 
it  was  abandoned  as  unfounded,  and  even  forgot- 
ten completely,  until  revived  again  about  the  mid- 
dle of  the  ipth  century.  During  this  century 
of  wonder  a  sufficiency  of  exactness  was,  how- 
ever, introduced  into  the  study  of  microscopic  or- 
ganisms to  call  for  the  use  of  names,  and  we  find 
Muller  using  the  names  of  Monas,  Proteus,  Vibrio, 
Bacillus,  and  Spirillum,  names  which  still  continue 
in  use,  although  commonly  with  a  different  signifi- 
cance from  that  given  them  by  Muller.  Muller 
did  indeed  make  a  study  sufficient  to  recognise 
the  several  distinct  types,  and  attempted  to  clas- 
sify these  bodies.  They  were  not  regarded  as  of 
much  importance,  but  simply  as  the  most  minute 
organisms  known. 

Nothing  of  importance  came  from  this  work, 
however,  partly  because  of  the  inadequacy  of  the 
microscopes  of  the  day,  and  partly  because  of  a 
failure  to  understand  the  real  problems  at  issue. 
When  we  remember  the  minuteness  of  the  bacteria, 
the  impossibility  of  studying  any  one  of  them  for 
more  than  a  few  moments  at  a  time — only  so  long, 
in  fact,  as  it  can  be  followed  under  a  microscope; 
when  we  remember,  too,  the  imperfection  of  the 


12  THE  STORY  OF  GERM  LIFE. 

compound  microscopes  which  made  high  powers 
practical  impossibilities ;  and,  above  all,  when  we 
appreciate  the  looseness  of  the  ideas  which  per- 
vaded all  scientists  as  to  the  necessity  of  accurate 
observation  in  distinction  from  inference,  it  is  not 
strange  that  the  last  century  gave  us  no  knowl- 
edge of  bacteria  beyond  the  mere  fact  of  the  ex- 
istence of  some  extremely  minute  organisms  in 
different  decaying  materials.  Nor  did  the  iQth 
century  add  much  to  this  until  toward  its  middle. 
It  is  true  that  the  microscope  was  vastly  improved 
early  in  the  century,  and  since  this  improvement 
served  as  a  decided  stimulus  to  the  study  of  mi- 
croscopic life,  among  other  organisms  studied, 
bacteria  received  some  attention.  Ehrenberg, 
Dujardin,  Fuchs,  Perty,  and  others  left  the  im- 
press of  their  work  upon  bacteriology  even  before 
the  middle  of  the  century.  It  is  true  that  Schwann 
shrewdly  drew  conclusions  as  to  the  relation  of 
microscopic  organisms  to  various  processes  of 
fermentation  and  decay — conclusions  which,  al- 
though not  accepted  at  the  time,  have  subse- 
quently proved  to  be  correct.  It  is  true  that 
Fuchs  made  a  careful  study  of  the  infection  of 
"  blue  milk,"  reaching  the  correct  conclusion  that 
the  infection  was  caused  by  a  microscopic  organ- 
ism which  he  discovered  and  carefully  studied. 
It  is  true  that  Henle  made  a  general  theory  as  to 
the  relation  of  such  organisms  to  diseases,  and 
pointed  out  the  logically  necessary  steps  in  a  dem- 
onstration of  the  causal  connection  between  any 
organism  and  a  disease.  It  is  true  also  that  a 
general  theory  of  the  production  of  all  kinds  of 
fermentation  by  living  organisms  had  been  ad- 
vanced. But  all  these  suggestions  made  little 
impression.  On  the  one  hand,  bacteria  were  not 


BACTERIA  AS  PLANTS.  13 

recognised  as  a  class  of  organisms  by  themselves 
— were  not,  indeed,  distinguished  from  yeasts  or 
other  minute  animalculae.  Their  variety  was  not 
mistrusted  and  their  significance  not  conceived. 
As  microscopic  organisms,  there  were  no  reasons 
for  considering  them  of  any  more  importance 
than  any  other  small  animals  or  plants,  and  their 
extreme  minuteness  and  simplicity  made  them  of 
little  interest  to  the  microscopist.  On  the  other 
hand,  their  causal  connection  with  fermentative 
and  putrefactive  processes  was  entirely  obscured 
by  the  overshadowing  weight  of  the  chemist  Lie- 
big,  who  believed  that  fermentations  and  putre- 
factions were  simply  chemical  processes.  Liebig 
insisted  that  all  albuminoid  bodies  were  in  a 
state  of  chemically  unstable  equilibrium,  and  if 
left  to  themselves  would  fall  to  pieces  without 
any  need  of  the  action  of  microscopic  organisms. 
The  force  of  Liebig's  authority  and  the  brilliancy 
of  his  expositions  led  to  the  wide  acceptance  of 
his  views  and  the  temporary  obscurity  of  the  re- 
lation of  microscopic  organisms  to  fermentative 
and  putrefactive  processes.  The  objections  to 
Liebig's  views  were  hardly  noticed,  and  the  force 
of  the  experiments  of  Schwann  was  silently  ig- 
nored. Until  the  sixth  decade  of  the  century,, 
therefore,  these  organisms,  which  have  since  be- 
come the  basis  of  a  new  branch  of  science,  had 
hardly  emerged  from  obscurity.  A  few  micros- 
copists  recognised  their  existence,  just  as  they 
did  any  other  group  of  small  animals  or  plants, 
but  even  yet  they  failed  to  look  upon  them  as 
forming  a  distinct  group.  A  growing  number  of 
observations  was  accumulating,  pointing  toward 
a  probable  causal  connection  between  fermenta- 
tive and  putrefactive  processes  and  the  growth  of 


14  THE  STORY  OF  GERM  LIFE. 

microscopic  organisms ;  but  these  observations 
were  known  only  to  a  few,  and  were  ignored  by 
the  majority  of  scientists. 

It  was  Louis  Pasteur  who  brought  bacteria  to 
the  front,  and  it  was  by  his  labours  that  these  or- 
ganisms were  rescued  from  the  obscurity  of  scien- 
tific publications  and  made  objects  of  general  and 
crowning  interest.  It  was  Pasteur  who  first  suc- 
cessfully combated  the  chemical  theory  of  fer- 
mentation by  showing  that  albuminous  matter 
had  no  inherent  tendency  to  decomposition.  It 
was  Pasteur  who  first  clearly  demonstrated  that 
these  little  bodies,  like  all  larger  animals  and 
plants,  come  into  existence  only  by  ordinary 
methods  of  reproduction,  and  not  by  any  sponta- 
neous generation,  as  had  been  earlier  claimed. 
It  was  Pasteur  who  first  proved  that  such  a  com- 
mon phenomenon  as  the  souring  of  milk  was  pro- 
duced by  microscopic  organisms  growing  in  the 
milk.  It  was  Pasteur  who  first  succeeded  in  dem- 
onstrating that  certain  species  of  microscopic  or- 
ganisms are  the  cause  of  certain  diseases,  and  in 
suggesting  successful  methods  of  avoiding  them. 
All  these  discoveries  were  made  in  rapid  succes- 
sion. Within  ten  years  of  the  time  that  his  name 
began  to  be  heard  in  this  connection  by  scien- 
tists, the  subject  had  advanced  so  rapidly  that 
it  had  become  evident  that  here  was  a  new 
subject  of  importance  to  the  scientific  world,  if 
not  to  the  public  at  large.  The  other  important 
discoveries  which  Pasteur  made  it  is  not  our  pur- 
pose to  mention  here.  His  claim  to  be  consid- 
ered the  founder  of  bacteriology  will  be  recog- 
nised from  what  has  already  been  mentioned. 
It  was  not  that  he  first  discovered  the  organisms, 
or  first  studied  them ;  it  was  not  that  he  first  sug- 


BACTERIA  AS   PLANTS.  15 

gested  their  causal  connection  with  fermentation 
and  disease,  but  it  was  because  he  for  the  first  time 
placed  the  subject  upon  a  firm  foundation  by  prov- 
ing with  rigid  experiment  some  of  the  suggestions 
made  by  others,  and  in  this  way  turned  the  atten- 
tion of  science  to  the  study  of  micro-organisms. 

After  the  importance  of  the  subject  had  been 
demonstrated  by  Pasteur,  others  turned  their  at- 
tention Jn  the  same  direction,  either  for  the  pur- 
pose of  verification  or  refutation  of  Pasteur's 
views.  The  advance  was  not  very  rapid,  however, 
since  bacteriological  experimentation  proved  to  be 
a  subject  of  extraordinary  difficulty.  Bacteria 
were  not  even  yet  recognised  as  a  group  of  organ- 
isms distinct  enough  to  be  grouped  by  themselves, 
but  were  even  by  Pasteur  at  first  confounded  with 
yeasts.  As  a  distinct  group  of  organisms  they 
were  first  distinguished  by  Hoffman  in  1869,  since 
which  date  the  term  bacteria,  as  applying  to  this 
special  group  of  organisms,  has  been  coming 
more  and  more  into  use.  So  difficult  were  the 
investigations,  that  for  years  there  were  hardly 
any  investigators  besides  Pasteur  who  could  suc- 
cessfully handle  the  subject  and  reach  conclu- 
sions which  could  stand  the  test  of  time.  For  the 
next  thirty  years,  although  investigators  and  in- 
vestigations continued  to  increase,  we  can  find 
little  besides  dispute  and  confusion  along  this 
line.  The  difficulty  of  obtaining  for  experiment 
any  one  kind  of  bacteria  .by  itself,  unmixed  with 
others  (pure  cultures),  rendered  advance  almost 
impossible.  So  conflicting  were  the  results  that 
the  whole  subject  soon  came  into  almost  hopeless 
confusion,  and  very  few  steps  were  taken  upon 
any  sure  basis.  So  difficult  were  the  methods,  so 
contradictory  and  confusing  the  results,  because 


1 6  THE  STORY  OF  GERM   LIFE. 

of  impure  cultures,  that  a  student  of  to-day  who 
wishes  to  look  up  the  previous  discoveries  in 
almost  any  line  of  bacteriology  need  hardly  go 
back  of  1880,  since  he  can  almost  rest  assured 
that  anything  done  earlier  than  that  was  more 
likely  to  be  erroneous  than  correct. 

The  last  fifteen  years  have,  however,  seen  a 
wonderful  change.  The  difficulties  had  been 
mostly  those  of  methods  of  work,  and  with  the 
ninth  decade  of  the  century  these  methods  were 
simplified  by  Robert  Koch.  This  simplification 
of  method  for  the  first  time  placed  this  line  of 
investigation  within  the  reach  of  scientists  who 
did  not  have  the  genius  of  Pasteur.  It  was  now 
possible  to  get  pure  cultures  easily,  and  to  obtain 
with  such  pure  cultures  results  which  were  uni- 
form and  simple.  It  was  now  possible  to  take 
steps  which  had  the  stamp  of  accuracy  upon 
them,  and  which  further  experiment  did  not  dis- 
prove. From  the  time  when  these  methods  were 
thus  made  manageable  the  study  of  bacteria  in- 
creased with  a  rapidity  which  has  been  fairly 
startling,  and  the  information  which  has  accumu- 
lated is  almost  formidable.  The  very  rapidity 
with  which  the  investigations  have  progressed 
has  brought  considerable  confusion,  from  the  fact 
that  the  new  discoveries  have  not  had  time  to 
be  properly  assimilated  into  knowledge.  To- 
day many  facts  are  known  whose  significance  is 
still  uncertain,  and  a  clear  logical  discussion  of 
the  facts  of  modern  bacteriology  is  not  possible. 
But  sufficient  knowledge  has  been  accumulated  and 
digested  to  show  us  at  least  the  direction  along 
which  bacteriological  advance  is  tending,  and  it 
is  to  the  pointing  out  of  these  directions  that  the 
following  pages  will  be  devoted. 


BACTERIA  AS   PLANTS.  17 

WHAT  ARE  BACTERIA  ? 

The  most  interesting  facts  connected  with  the 
subject  of  bacteriology  concern  the  powers  and 
influence  in  Nature  possessed  by  the  bacteria. 
The  morphological  side  of  the  subject  is  interest- 
ing enough  to  the  scientist,  but  to  him  alone. 
Still,  it  is  impossible  to  attempt  to  study  the 
powers  of  bacteria  without  knowing  something  of 
the  organisms  themselves.  To  understand  how 
they  come  to  play  an  important  part  in  Nature's 
processes,  we  must  know  first  how  they  look  and 
where  they  are  found.  A  short  consideration  of 
certain  morphological  facts  will  therefore  be 
necessary  at  the  start. 

FORM    OF    BACTERIA. 

In  shape  bacteria  are  the  simplest  conceivable 
structures.  Although  there  are  hundreds  of  dif- 
ferent species,  they  have  only  three  general  forms, 
which  have  been  aptly  compared  to  billiard  balls, 
lead  pencils,  and  corkscrews.  Spheres,  rods,  and 
spirals  represent  all  shapes.  The  spheres  may  be 
large  or  small,  and  may  group  themselves  in  va- 
rious ways;  the  rods  may  be  long  or  short,  thick 
or  slender;  the  spirals  may  be  loosely  or  tightly 
coiled,  and  may  have  only  one  or  two  or  may 
have  many  coils,  and  they  may  be  flexible  or 
stiff ;  but  still  rods,  spheres,  and  spirals  comprise 
all  types  (Fig.  i). 

In  size  there  is  some  variation,  though  not 
very  great.  All  are  extremely  minute,  and  never 
visible  to  the  naked  eye.  The  spheres  vary  from 
0.25  p.  to  1.5  p.  (0.000012  to  0.00006  inches).  The 
rods  may  be  no  more  than  0.3  p.  in  diameter, 
or  may  be  as  wide  as  1.5  /A  to  2.5  y,  and  in  length 


i8 


THE  STORY  OF  GERM   LIFE. 


vary  all  the  way  from  a  length  scarcely  longer 
than  their  diameter  to  long  threads.  About  the 
same  may  be  said  of  the  spi- 
ral forms.  They  are  decid- 
edly the  smallest  living  or- 
ganisms which  our  micro- 
scopes have  revealed. 

In  their  method  of  growth 

we  ^nc*  one  °^  t^ie  most  cnar- 
acteristic      features.      They 

universally  have  the    power 
of  multiplication    by  simple 
division  or  fission.     Each  in- 
dividual elongates  and  then 
divides   in    the   middle   into 
FIG.   i.-General  shapes  tw°   similar  halves,  each  of 
of  bacteria :  a,  spheri-  which  then  repeats  the  pro- 
cai  forms  ;  b,   Rod-  cess.      This  method  of  mul- 
rarfoerms?rmS;  C'    P'"  tiplication  by  simple  division 
is    the   distinguishing    mark 

which  separates  the  bacteria  from  the  yeasts,  the 
latter  plants  multiplying  by  a  process  known  as 
budding.  Fig.  2  shows  these  two  methods  of 
multiplication. 

While  all  bacteria  thus  multiply  by  division, 
certain  differences  in  the  details  produce  rather 
striking  differences  in  the  results.  Considering 
first  the  spherical  forms,  we  find  that  some  species 
divide,  as  described,  into  two,  which  separate  at 
once,  and  each  of  which  in  turn  divides  in  the  op- 
posite direction,  called  Micrococcus,  (Fig.  3).  Other 
species  divide  only  in  one  direction.  Frequently 
they  do  not  separate  after  dividing,  but  remain 
attached.  Each,  however,  again  elongates  and  di- 
vides again,  but  all  still  remain  attached.  There 
are  thus  formed  long  chains  of  spheres  like  strings 


BACTERIA  AS   PLANTS. 


of  beads,  called  Streptococci  (Fig.  4).  Other  species 
divide  first  in  one  direction,  then  at  right  angles 
to  the  first  division,  and  a  third  division  follows  at 
right  angles  to 
the  plane  of 
the  first  two, 
thus  producing 
solid  groups  of 
fours,  eights, 
or  sixteens 
(Fig.  5),  called 
Sarcina.  Each 
different  spe- 
cies of  bacteria 
is  uniform  in 
its  method  of 
division,  and 
these  differen- 
ces are  there- 
fore indica- 
tions of  differ- 


FIG.  2. — Method  of  multiplication  of  bacte- 
ria :  a  and  b,  Bacteria  dividing  by  fis- 
sion ;  c,  A  yeast  multiplying  by  budding. 


ences    in    spe- 
cies,  or,   according   to    our    present   method  of 
classification,  the    different  methods  of  division 


FIG.  3. — Micrococci. 


FIG.  4. — Streptococci. 


represent  different  genera.     All  bacteria  produ- 
cing Streptococcus  chains  form  a  single  genus  Strep- 


20 


THE   STORY  OF   GERM   LIFE. 


tococcus,    and    all    which  divide    in  three  division 
planes  form  another  genus,  Sarcina,  etc. 


FIG.  5.— Sarcina. 


FIG.  6.  —  Separate  rods 
showing  variations  in 
size,  magnified  about 
1000  diameters. 


The  rod-shaped  bacteria  also  differ  somewhat, 
but  to  a  less  extent.  They  almost  always  divide 
in  a  plane  at  right  angles  to  their  longest  dimen- 
sion. But  here  again  we  find  some  species  sepa- 
rating immediately  after  division,  and  thus  always 
appearing  as  short  rods  (Fig.  6),  while  others 

remain  attached 
after  division 
and  form  long 
chains.  Some- 
times they  ap- 
pear to  continue 
to  increase  in 
length  without 
showing  any 
signs  of  divis- 
FIG.  7.— Rod-forms  united  to  form  chains,  ion,  and  in  this 

way  long  threads 

are  formed  (Fig.  7).  These  threads  are,  however, 
potentially  at  least,  long  chains  of  short  rods,  and 
under  proper  conditions  they  will  break  up  into 
such  short  rods,  as  shown  in  Fig.  7  a.  Occasion- 
ally a  rod  species  may  divide  lengthwise,  but  this 
is  rare.  Exactly  the  same  may  be  said  of  the 


BACTERIA  AS   PLANTS. 


21 


spiral  forms.     Here,  too,  we  find  short  rods  and 
long  chains,  or  long  spiral  filaments  in  which  can 
be   seen    no    division 
into  shorter  elements, 
but  which,  under  cer- 
tain conditions,  break 
up  into  short  sections 
(Fig.  8). 

RAPIDITY    OF 
MULTIPLICATION. 

It  is  this  power  of 
multiplication  by  di- 
vision that  makes  bac- 
teria agents  of  such 
significance.  Their 
minute  size  would 
make  them  harmless 
enough  if  it  were  not 
tor  an  extraordinary 
power  of  multiplica- 
tion. This  power  of 
growth  and  division 
is  almost  incredible. 
Some  of  the  species 
which  have  been  care- 
fully watched  under 

the  microscope  have  been  found  under  favourable 
conditions  to  grow  so  rapidly  as  to  divide  every 
half  hour,  or  even  less.  The  number  of  offspring 
that  would  result  in  the  course  of  twenty-four 
hours  at  this  rate  is  of  course  easily  computed. 
In  one  day  each  bacterium  would  produce  over 
16,500,000  descendants,  and  in  two  days  about 
281,500,000,000.  It  has  been  further  calculated 


FIG.  8. — Various  types  of  spiral 
bacteria. 


22  THE  STORY  OF   GERM   LIFE. 

that  these  281,500,000,000  would  form  about  a 
solid  pint  of  bacteria  and  weigh  about  a  pound. 
At  the  end  of  the  third  day  the  total  descendants 
would  amount  to  47,000,000,000,000,  and  would 
weigh  about  16,000,000  pounds.  Of  course  these 
numbers  have  no  significance,  for  they  are  never 
actual  or  even  possible  numbers.  Long  before 
the  offspring  reach  even  into  the  millions  their 
rate  of  multiplication  is  checked  either  by  lack  of 
food  or  by  the  accumulation  of  their  own  ex- 
creted products,  which  are  injurious  to  them.  But 
the  figures  do  have  interest  since  they  show  faint- 
ly what  an  unlimited  power  of  multiplication  these 
organisms  have,  and  thus  show  us  that  in  dealing 
with  bacteria  we  are  dealing  with  forces  of  al- 
most infinite  extent. 

This  wonderful  power  of  growth  is  chiefly  due 
to  the  fact  that  bacteria  feed  upon  food  which  is 
highly  organized  and  already  in  condition  for  ab- 
sorption. Most  plants  must  manufacture  their 
own  foods  out  of  simpler  substances,  like  carbonic 
dioxide  (CO2)  and  water,  but  bacteria,  as  a  rule, 
feed  upon  complex  organic  material  already  pre- 
pared by  the  previous  life  of  plants  or  animals. 
For  this  reason  they  can  grow  faster  than  other 
plants.  Not  being  obliged  to  make  their  own 
foods  like  most  plants,  nor  to  search  for  it  like 
animals,  but  living  in  its  midst,  their  rapidity  of 
growth  and  multiplication  is  limited  only  by  their 
power  to  seize  and  assimilate  this  food.  As  they 
grow  in  such  masses  of  food,  they  cause  certain 
chemical  changes  to  take  place  in  it,  changes 
doubtless  directly  connected  with  their  use  of  the 
material  as  food.  Recognising  that  they  do 
cause  chemical  changes  in  food  material,  and  re- 
membering this  marvellous  power  of  growth,  we 


BACTERIA  AS   PLANTS. 


are  prepared  to  believe  them  capable  of  producing 
changes  wherever  they  get  a  foothold  and  begin 
to  grow.  Their  power  of  feeding  upon  com- 
plex organic  food 
and  producing  chemi- 
cal changes  therein, 
together  with  their 
marvellous  power  of 
assimilating  this  ma- 
terial as  food,  make 
them  agents  in  Na- 


ture  of   extreme 
portance. 


im- 


FIG.  9.— Showing  various  shaped 
rods. 


DIFFERENCES    BETWEEN    DIFFERENT    SPECIES    OF 
BACTERIA. 

While  bacteria  are  thus  very  simple  in  form, 

there  are  a  few 
other  slight  varia- 
tions in  detail 
which  assist  in  dis- 
(a  tinguishing  them. 
The  rods  are  some- 
times very  blunt  at 
the  ends,  almost 
as  if  cut  square 
across,  while  in 
other  species  they 
are  more  rounded 
and  occasionally 

slightly      tapering 
FIG.  10. — Bacteria  surrounded  by  cap-     /T?-_     *   \          o~     *T 
sules:  a  and  b  represent  zoogloea;     lrig-     9)-        SOme- 

c,  Chains  of  cocci  with  a  capsule ;    times  they  are  sur- 

d,  Bacteria  showing  the   supposed    roun(ied   by  a   thin 
structure  in  which  x  is  the  nucleus,    ,  r        •>          . 

and  y  the  protoplasm.  layer  or  some  gelat- 


THE  STORY  OF  GERM   LIFE. 


inous  substance,  which  forms  what  is  called  a 
capsule  (Fig.  10).  This  capsule  may  connect  them 
and  serve  as  a  cement,  to  prevent  the  separate 
elements  of  a  chain  from  falling  apart  (Fig.  10  c]. 

Sometimes  such 
a  gelatinous  se- 
cretion will  unite 
great  masses  of 
bacteria  into 
clusters,  which 
may  float  on  the 
surface  of  the 
liquid  in  which 
they  grow  or 
may  sink  to  the 
bottom.  Such 
masses  are  called 
z00gfaa,and  their 
general  appear- 
ance serves  as 
one  of  the  char- 
acters for  distin- 
guishing differ- 
ent species  of 

FIG.  ii.— Various  types  of  bacteria  "colo-  bacteria  (Fig.  10, 
nies "  formed  when  growing  in  nutrient  a  and  fr).  When 
gelatine.  Each  different  type  of  colony  wi  n  P-  i  n  solid 

is  produced  by  a  different  species  of   growing  in    SOI 
bacterium.  media,  such  as  a 

nutritious  liquid 

made  stiff  with  gelatine,  the  different  species  have 
different  methods  of  spreading  from  their  central 
point  of  origin.  A  single  bacterium  in  the  midst 
of  such  a  stiffened  mass  will  feed  upon  it  and  pro- 
duce descendants  rapidly  ;  but  these  descendants, 
not  being  able  to  move  through  the  gelatine,  will 
remain  clustered  together  in  a  mass,  which  the 


BACTERIA  AS   PLANTS.  25 

bacteriologist  calls  a  colony.  But  their  method  of 
clustering,  due  to  different  methods  of  growth,  is 
by  no  means  always  alike,  and  these  colonies 
show  great  differences  in  general  appearance. 
The  differences  appear  to  be  constant,  however, 
for  the  same  species  of  bacteria,  and  hence  the 
shape  and  appearance  of  the  colony  enable  bac- 
teriologists to  discern  different  species  (Fig.  n). 
All  these  points  of  difference  are  of  practical  use 
to  the  bacteriologist  in  distinguishing  species. 

SPORE    FORMATION. 

In  addition  to  their  power  of  reproduction  by 
simple  division,  many  species  of  bacteria  have  a 
second  method  by  means  of  spores.  Spores  are 
special  rounded  or  oval  bits  of  bacteria  protoplasm 
capable  of  resisting  adverse  conditions  which 
would  destroy  the  ordinary  bacteria.  They  arise 
among  bacteria  in  two  different  methods. 

Endogenous  spores. — These  spores  arise  inside 
of  the  rods  or  the  spiral  forms  (Fig.  12).  They 
first  appear  as  slight  granular  masses,  or  as  dark 
points  which  become  gradually  distinct  from  the 
rest  of  the  rod.  Eventually  there  is  thus  formed 
inside  the  rod  a  clear,  highly  refractive,  spherical 
or  oval  spore,  which  may  even  be  of  a  greater 
diameter  than  the  rod  producing  it,  thus  causing 
it  to  swell  out  and  become  spindle  formed  (Fig. 
12  c].  These  spores  may  form  in  the  middle  or  at 
the  ends  of  the  rods  (Fig.  12).  They  may  use  up 
all  the  protoplasm  of  the  rod  in  their  formation, 
or  they  may  use  only  a  small  part  of  it,  the  rod 
which  forms  them  continuing  its  activities  in  spite 
of  the  formation  of  the  spores  within  it.  They  are 
always  clear  and  highly  refractive  from  contain- 


26 


THE  STORY  OF  GERM   LIFE. 


ing  little  water,  and  they  do  not  so  readily  absorb 
staining  material  as  the  ordinary  rods.  They  ap- 
pear to  be  covered  with  a  layer  of  some  substance 
which  resists  the  stain,  and  which  also  enables 

them  to  resist  vari- 
ous external  agen- 
cies. This  protect- 
ive covering,  to- 
gether with  their 
small  amount  of 
water,  enables  them 
to  resist  almost  any 
amount  of  drying, 
a  high  degree  of 
heat,  and  many 
other  adverse  con- 
ditions. Common- 
ly the  spores  break 
out  of  the  rod,  and 
the  rod  producing 
them  dies,  although 
sometimes  the  rod 
may  continue  its 
FIG.  12. — Endogenous  spores :  a  and  activity  even  after 
b,  Spores  forming  at  intervals  in  f^  cnnr^Q  hav^ 
the  rods  ;  c,  Spores  forming  in  the  tne  sPores  nave 
middle  of  the  rods  and  causing  the  been  produced, 
middle  to  swell;  d,  Spores  form-  ^  rthrogeilOUS 

ing  at   the  end  of  the  rods  and  /w        r*     '•• 

causing  the  end  to  swell.  Spores   (?)  .—Certain 

species  of  bacteria 

do  not  produce  spores  as  just  described,  but 
may  give  rise  to  bodies  that  are  sometimes  called 
arthrospores.  These  bodies  are  formed  as  short 
segments  of  rods  (Fig.  130).  A  long  rod  may 
sometimes  break  up  into  several  short  rounded 
elements,  which  are  clear  and  appear  to  have  a 
somewhat  increased  power  of  resisting  adverse 


BACTERIA  AS   PLANTS. 


conditions.      The  same  may  happen  among  the 

spherical  forms,  which  only  in  rare  instances  form 

endogenous  spores. 

Among  the  spheres 

which  form  a  chain 

of  streptococci  some 

may  occasionally  be 

slightly       different 

from  the  rest.  They 

are   a   little  larger, 

and      have       been 

thought  to  have  an 

increased    resisting 

power   like  that  of 

true  spores  (Fig.  13    FIG.     13.  —  So  -  called    arthrogenous 

&}.    It  is  quite  doubt-  spores:   a,   Forming  as  segments 

f ul,  however,  wheth-  °ff  ^  b' As segments of  a  chain 
er  it  is  proper  to  re- 
gard these  bodies  as  spores.  There  is  no  good 
evidence  that  they  have  any  special  resisting 
power  to  heat  like  endogenous  spores,  and  bac- 
teriologists in  general  are  inclined  to  regard  them 
simply  as  resting  cells.  The  term  arthrospores 
has  been  given  to  them  to  indicate  that  they  are 
formed  as  joints  or  segments,  and  this  term  may 
be  a  convenient  one  to  retain  although  the  bodies 
in  question  are  not  true  spores. 

Still  a  different  method  of  spore  formation 
occurs  in  a  few  peculiar  bacteria.  In  this  case 
(Fig.  14)  the  protoplasm  in  the  large  thread  breaks 
into  many  minute  spherical  bodies,  which  finally 
find  exit.  The  spores  thus  formed  may  not  be  all 
alike,  differences  in  size  being  noticed.  This 
method  of  spore  formation  occurs  only  in  a  few 
special  forms  of  bacteria. 

The  matter  of  spore  formation  serves  as  one 


28 


THE   STORY   OF  GERM    LIFE. 


of  the  points  for  distinguishing  species.  Some 
species  do  not  form  spores,  at  least  under  any  of 
the  conditions  in  which  they  have  been  studied. 
Others  form  them  readily  in  almost  any  condition, 
and  others  again  only  under  special  conditions 
which  are  adverse  to  their 
life.  The  method  of  spore 
formation  is  always  uni- 
form for  any  single  species. 
Whatever  be  the  method 
of  the  formation  of  the 
spore,  its  purpose  in  the 
life  of  the  bacterium  is  al- 
ways the  same.  It  serves 
as  a  means  of  keeping  the 
species  alive  under  condi- 
tions of  adversity.  Its 
power  of  resisting  heat  or 
drying  enables  it  to  live 
where  the  ordinary  active 
14.  —  Formation  of  forms  would  be  speedily 
killed.  Some  of  these 
spores  are  capable  of  re- 
sisting a  heat  of  180°  C.  (360°  F.)  for  a  short  time, 
and  boiling  water  they  can  resist  for  a  long  time. 
Such  spores  when  subsequently  placed  under  fa- 
vourable conditions  will  germinate  and  start  bac- 
terial activity  anew. 


FIG. 


spores  in  unusual  forms 
(Crenothrix}. 


MOTION. 


Some  species  of  bacteria  have  the  power  of 
active  motion,  and  may  be  seen  darting  rapidly 
to  and  fro  in  the  liquid  in  which  they  are  grow- 
ing. This  motion  is  produced  by  flagella  which 
protrude  from  the  body.  These  flagella  (Fig.  15) 


BACTERIA  AS   PLANTS.  29 

arise  from  a  membrane  surrounding  the  bacterium, 
but  have  an  intimate  connection  with  the  proto- 


FlG.  15. — Bacteria  provided  with  flagella  :  a,  Single  flagellum  ;  b, 
Two  flagella;  c,  A  tuft  of  flagella  at  one  end;  d,  Tufts  of 
flagella  at  both  ends ;  e,  Uniform  covering  of  flagella ;  f, 
Showing  the  origin  of  flagella  from  the  outer  layer  of  the  body. 

plasmic  content.     Their  distribution  is   different 
in   different  species  of  bacteria.      Some    species 


3° 


THE  STORY  OF  GERM   LIFE. 


have  a  single  flagellum  at  one  end  (Fig.  150). 
Others  have  one  at  each  end  (Fig.  15  b).  Others, 
again,  have,  at  least  just  before  dividing,  a  bunch 
at  one  or  both  ends  (Fig.  15  c  and  d),  while  others, 
again,  have  many  flagella  distributed  all  over  the 
body  in  dense  profusion  (Fig.  15  e).  These  flagella 
keep  up  a  lashing  to  and  fro  in  the  liquid,  and  the 
lashing  serves  to  propel  the  bacteria  through  the 
liquid. 

INTERNAL    STRUCTURE. 

It  is  hardly  possible  to  say  much  about  the 
structure  of  the  bacteria  beyond  the  description 
of  their  external  forms.  With  all  the  variations 
in  detail  mentioned,  they  are 
extraordinarily  simple,  and 
about  all  that  can  be  seen  is 
their  external  shape.  Of 
course,  they  have  some  in- 
ternal structure,  but  we 
know  very 'little  in  regard  to 
it.  Some  microscopists  have 
described  certain  appearan- 
ces which  they  think  indi- 
cate internal  structure.  Fig. 
16  shows  some  of  these  ap- 
pearances. The  matter  is  as 
yet  very  obscure,  however. 
The  bacteria  appear  to  have 
a  membranous  covering 
which  sometimes  is  of  a  cel- 
lulose nature.  Within  it  is 
protoplasm  which  shows  various  uncertain  ap- 
pearances. Some  microscopists  have  thought 
they  could  find  a  nucleus,  and  have  regarded 
bacteria  as  cells  with  inclosed  nucleii  (Figs.  10  a 


FIG.    16.  —  Internal  struc- 
ture of  bacteria. 


BACTERIA  AS   PLANTS.  31 

and  i5/).  Others  have  regarded  the  whole  bac- 
terium as  a  nucleus  without  any  protoplasm, 
while  others,  again,  have  concluded  that  the  dis- 
cerned internal  structure  is  nothing  except  an  ap- 
pearance presented  by  the  physical  arrangement  of 
the  protoplasm.  While  we  may  believe  that  they 
have  some  internal  structure,  we  must  recognise 
that  as  yet  microscopists  have  not  been  able  to 
make  it  out.  In  short,  the  bacteria  after  two 
centuries  of  study  appear  to  us  about  as  they  did 
at  first.  They  must  still  be  described  as  minute 
spheres,  rods,  or  spirals,  with  no  further  discern- 
ible structure,  sometimes  motile  and  sometimes 
stationary,  sometimes  producing  spores  and  some- 
times not,  and  multiplying  universally  by  binary 
fission.  With  all  the  development  of  the  modern 
microscope  we  can  hardly  say  more  than  this. 
Our  advance  in  knowledge  of  bacteria  is  con- 
nected almost  wholly  with  their  methods  of  growth 
and  the  effects  they  produce  in  Nature. 

ANIMALS    OR    PLANTS  ? 

There  has  been  in  the  past  not  a  little  ques- 
tion as  to  whether  bacteria  should  be  rightly 
classed  with  plants  or  with  animals.  They  cer- 
tainly have  characters  which  ally  them  with  both. 
Their  very  common  power  of  active  independent 
motion  and  their  common  habit  of  living  upon 
complex  bodies  for  foods  are  animal  characters, 
and  have  lent  force  to  the  suggestion  that  they 
are  true  animals.  But  their  general  form,  their 
method  of  growth  and  formation  of  threads,  and 
their  method  of  spore  formation  are  quite  plant- 
like.  Their  general  form  is  very  similar  to  a 
group  of  low  green  plants  known  as  Oscillaria. 
3 


THE  STORY  OF  GERM  LIFE. 


Fig.  17  shows  a  group  of  these  Oscillariae,  and 
the  similarity  of  this  to  some  of  the  thread-like 

bacteria  is  de- 
cided. The  Os- 
cillarice  are,  how- 
ever, true  plants, 
and  are  of  a 
green  colour. 
Bacteria  are 
therefore  to-day 
looked  upon  as 
a  low  type  of 
plant  which  has 
no  chlorophyll,* 
but  is  related  to 
Oscillarice.  The 
absence  of  the 
chlorophyll  has 
forced  them  to 
adopt  new  rela- 
tions to  food, 
and  compels 

FIG.  17. — Threads  of  Oscillaria,  the  nearest    them       to       feed 
allies  of  bacteria. 

upon       complex 

foods  instead  of  the  simple  ones,  which  form  the 
food  of  green  plants.  We  may  have  no  hesita- 
tion, then,  in  calling  them  plants.  It  is  interest- 
ing to  notice  that  with  this  idea  their  place  in  the 
organic  world  is  reduced  to  a  small  one  systemat- 
ically. They  do  not  form  a  class  by  themselves, 
but  are  simply  a  subclass,  or  even  a  family,  and 
a  family  closely  related  to  several  other  common 
plants.  But  the  absence  of  chlorophyll  and  the 
resulting  peculiar  life  has  brought  about  a  curi- 


*  Chlorophyll  is  the  green  colouring  matter  of  plants. 


BACTERIA  AS   PLANTS.  33 

ous  anomaly.  Whereas  their  closest  allies  are 
known  only  to  botanists,  and  are  of  no  interest 
outside  of  their  systematic  relations,  the  bacteria 
are  familiar  to  every  one,  and  are  demanding  the 
life  attention  of  hundreds  of  investigators.  It  is 
their  absence  of  chlorophyll  and  their  consequent 
dependence  upon  complex  foods  which  has  pro- 
duced this  anomaly. 

CLASSIFICATION    OF    BACTERIA. 

While  it  has  generally  been  recognised  that 
bacteria  are  plants,  any  further  classification  has 
proved  a  matter  of  great  difficulty,  and  bacteriolo- 
gists find  it  extremely  difficult  to  devise  means  of 
distinguishing  species.  Their  extreme  simplicity 
makes  it  no  easy  matter  to  find  points  by  which 
any  species  can  be  recognised.  But  in  spite  of 
their  similarity,  there  is  no  doubt  that  many 
different  species  exist.  Bacteria  which  appear  to 
be  almost  identical,  under  the  microscope  prove 
to  have  entirely  different  properties,  and  must 
therefore  be  regarded  as  distinct  species.  But 
how  to  distinguish  them  has  been  a  puzzle. 
Microscopists  have  come  to  look  upon  the  differ- 
ences in  shape,  multiplication,  and  formation  of 
spores  as  furnishing  data  sufficient  to  enable 
them  to  divide  the  bacteria  into  genera.  The 
genus  Bacillus,  for  instance,  is  the  name  given  to 
all  rod-shaped  bacteria  which  form  endogenous 
spores,  etc.  But  to  distinguish  smaller  subdi- 
visions it  has  been  found  necessary  to  fall  back 
upon  other  characters,  such  as  the  shape  of  the 
colony  produced  in  solid  gelatine,  the  power  to 
produce  disease,  or  to  oxidize  nitrites,  etc.  Thus 
at  present  the  different  species  are  distinguished 


34  THE   STORY   OF  GERM   LIFE. 

rather  by  their  physiological  than  their  morpho- 
logical characters.  This  is  an  unsatisfactory 
basis  of  classification,  and  has  produced  much 
confusion  in  the  attempts  to  classify  bacteria. 
The  problem  of  determining  the  species  of  bac- 
teria is  to-day  a  very  difficult  one,  and  with 
our  best  methods  is  still  unsatisfactorily  solved. 
A  few  species  of  marked  character  are  well 
known,  and  their  powers  of  action  so  well  under- 
stood that  they  can  be  readily  recognised ;  but 
of  the  great  host  of  bacteria  studied,  the  large 
majority  have  been  so  slightly  experimented  upon 
that  their  characters  are  not  known,  and  it  is  im- 
possible, therefore,  to  distinguish  many  of  them 
apart.  We  find  that  each  bacteriologist  working 
in  any  special  line  commonly  keeps  a  list  of  the 
bacteria  which  he  finds,  with  such  data  in  re- 
gard to  them  as  he  has  collected.  Such  a  list  is 
of  value  to  him,  but  commonly  of  little  value  to 
other  bacteriologists  from  the  insufficiency  of  the 
data.  Thus  it  happens  that  a  large  part  of  the 
different  species  of  bacteria  described  in  literature 
to-day  have  been  found  and  studied  by  one  in- 
vestigator alone.  By  him  they  have  been  de- 
scribed and  perhaps  named.  Quite  likely  the 
same  species  may  have  been  found  by  two  or 
three  other  bacteriologists,  but  owing  to  the 
difficulty  of  comparing  results  and  the  incom- 
pleteness of  the  descriptions  the  identity  of  the 
species  is  not  discovered,  and  they  are  probably 
described  again  under  different  names.  The 
same  process  may  be  repeated  over  and  over 
again,  until  the  same  species  of  bacterium  will 
come  to  be  known  by  several  different  names,  as 
it  has  been  studied  by  different  observers. 


BACTERIA  AS  PLANTS.  35 

VARIATION    OF    BACTERIA. 

This  matter  is  made  even  more  confusing  by 
the  fact  that  any  species  of  bacterium  may  show 
more  or  less  variation.  At  one  time  in  the  his- 
tory of  bacteriology,  a  period  lasting  for  many 
years,  it  was  the  prevalent  opinion  that  there  was 
no  constancy  among  bacteria,  but  that  the  same 
species  might  assume  almost  any  of  the  various 
forms  and  shapes,  and  possess  various  properties. 
Bacteria  were  regarded  by  some  as  stages  in  the 
life  history  of  higher  plants.  This  question  as 
to  whether  bacteria  remain  constant  in  character 
for  any  considerable  length  of  time  has  ever  been 
a  prominent  one  with  bacteriologists,  and  even 
to-day  we  hardly  know  what  the  final  answer  will 
be.  It  has  been  demonstrated  beyond  perad- 
venture  that  some  species  may  change  their 
physiological  characters.  Disease  bacteria,  for 
instance,  under  certain  conditions  lose  their 
powers  of  developing  disease.  Species  which  sour 
milk,  or  others  which  turn  gelatine  green,  may 
lose  their  characters.  Now,  since  it  is  upon  just 
such  physiological  characters  as  these  that  we 
must  depend  in  order  to  separate  different  species 
of  bacteria  from  each  other,  it  will  be  seen  that 
great  confusion  and  uncertainty  will  result  in  our 
attempts  to  define  species.  Further,  it  has  been 
proved  that  there  is  sometimes  more  or  less  of  a 
metamorphosis  in  the  life  history  of  certain 
species  of  bacteria.  The  same  species  may  form 
a  short  rod,  or  a  long  thread,  or  break  up  into 
spherical  spores,  and  thus  either  a  short  rod,  or 
a  thread,  or  a  spherical  form  may  belong  to  the 
same  species.  Other  species  may  be  motile  at 
one  time  and  stationary  at  another,  while  at  a 


36  THE  STORY  OF  GERM   LIFE. 

third  period  it  is  a  simple  mass  of  spherical 
spores.  A  spherical  form,  when  it  lengthens 
before  dividing,  appears  as  a  short  rod,  and  a 
short  rod  form  after  dividing  may  be  so  short  as 
to  appear  like  a  spherical  organism. 

With  all  these  reasons  for  confusion,  it  is  not 
to  be  wondered  at  that  no  satisfactory  classifica- 
tion of  bacteria  has  been  reached,  or  that  differ- 
ent bacteriologists  do  not  agree  as  to  what  consti- 
tutes a  species,  or  whether  two  forms  are  identical 
or  not.  But  with  all  the  confusion  there  is  slowly 
being  obtained  something  like  system.  In  spite 
of  the  fact  that  species  may  vary  and  show 
different  properties  under  different  conditions, 
the  fundamental  constancy  of  species  is  every- 
where recognised  to-day  as  a  fact.  The  members 
of  the  same  species  may  show  different  properties 
under  different  conditions,  but  it  is  believed  that 
under  identical  conditions  the  properties  will  be 
constant.  It  is  no  more  possible  to  convert  one 
species  into  another  than  it  is  among  the  higher 
orders  of  plants.  It  is  believed  that  bacteria 
do  form  a  group  of  plants  by  themselves,  and 
are  not  to  be  regarded  as  stages  in  the  history 
of  higher  plants.  It  is  believed  that,  together 
with  a  considerable  amount  of  variability  and 
an  occasional  somewhat  long  life  history  with 
successive  stages,  there  is  also  an  essential  con- 
stancy. A  systematic  classification  has  been 
made  which  is  becoming  more  or  less  satisfactory. 
We  are  constantly  learning  more  and  more  of  the 
characters,  so  that  they  can  be  recognised  in 
different  places  by  different  observers.  It  is  the 
conviction  of  all  who  work  with  bacteria  that,  in 
spite  of  the  difficulties,  it  is  only  a  matter  of  time 
when  we  shall  have  a  classification  and  descrip- 


BACTERIA  AS   PLANTS.  37 

tion  of  bacteria  so   complete  as  to  characterize 
the  different  species  accurately. 

Even  with  our  present  incomplete  knowledge 
of  what  characterizes  a  species,  it  is  necessary  to 
use  some  names.  Bacteria  are  commonly  given  a 
generic  name  based  upon  their  microscopic  ap- 
pearance. There  are  only  a  few  of  these  names. 
Micrococcus,  Streptococcus,  Staphylococcus,  Sarcina, 
Bacterium,  Bacillus,  Spirillum,  are  all  the  names  in 
common  use  applying  to  the  ordinary  bacteria. 
There  are  a  few  others  less  commonly  used.  To 
this  generic  name  a  specific  name  is  commonly 
added,  based  upon  some  physiological  character. 
For  example,  Bacillus  typhosus  is  the  name  given 
to  the  bacillus  which  causes  typhoid  fever.  Such 
names  are  of  great  use  when  the  species  is  a  com- 
mon and  well-known  one,  but  of  doubtful  value 
for  less-known  species.  It  frequently  happens 
that  a  bacteriologist  makes  a  study  of  the  bac- 
teria found  in  a  certain  locality,  and  obtains  thus 
a  long  list  of  species  hitherto  unknown.  In  these 
cases  it  is  common  simply  to  number  these  spe- 
cies rather  than  name  them.  This  method  is  fre- 
quently advisable,  since  the  bacteriologist  can 
seldom  hunt  up  all  bacteriological  literature  with 
sufficient  accuracy  to  determine  whether  some 
other  bacteriologist  may  not  have  found  the 
same  species  in  an  entirely  different  locality. 
One  bacteriologist,  for  example,  finds  some  sev- 
enty different  species  of  bacteria  in  different 
cheeses.  He  studies  them  enough  for  his  own 
purposes,  but  not  sufficiently  to  determine  whether 
some  other  person  may  not  have  found  the  same 
species  perhaps  in  milk  or  water.  He  therefore  sim- 
ply numbers  them — a  method  which  conveys  no 
suggestion  as  to  whether  they  may  be  new  species 


38  THE   STORY  OF  GERM   LIFE. 

or  not.  This  method  avoids  the  giving  of  separate 
names  to  the  same  species  found  by  different 
observers,  and  it  is  hoped  that  gradually  accumu- 
lating knowledge  will  in  time  group  together  the 
forms  which  are  really  identical,  but  which  have 
been  described  by  different  observers. 

WHERE    BACTERIA    ARE    FOUND. 

There  are  no  other  plants  or  animals  so  uni- 
versally found  in  Nature  as  the  bacteria.  It  is 
this  universal  presence,  together  with  their  great 
powers  of  multiplication,  which  renders  them  of 
so  much  importance  in  Nature.  They  exist  almost 
everywhere  on  the  surface  of  the  earth.  They 
are  in  the  soil,  especially  at  its  surface.  They  do 
not  extend  to  very  great  depths  of  soil,  however, 
few  existing  below  four  feet  of  soil.  At  the  sur- 
face they  are  very  abundant,  especially  if  the  soil 
is  moist  and  full  of  organic  material.  The  num- 
ber may  range  from  a  few  hundred  to  one  hun- 
dred millions  per  gramme.*  The  soil  bacteria 
vary  also  in  species,  some  twoscore  different  spe- 
cies having  been  described  as  common  in  soil. 
They  are  in  all  bodies  of  water,  both  at  the 
surface  and  below  it.  They  are  found  at  con- 
siderable depths  in  the  ocean.  All  bodies  of  fresh 
water  contain  them,  and  all  sediments  in  such 
bodies  of  water  are  filled  with  bacteria.  They 
are  in  streams  of  running  water  in  even  greater 
quantity  than  in  standing  water.  This  is  simply 
because  running  streams  are  being  constantly 
supplied  with  water  which  has  been  washing  the 
surface  of  the  country  and  thus  carrying  off  all 

*  One  gramme  is  fifteen  grains. 


BACTERIA  AS  PLANTS.  39 

surface  accumulations.  Lakes  or  reservoirs,  how- 
ever, by  standing  quiet  allow  the  bacteria  to  set- 
tle to  the  bottom,  and  the  water  thus  gets  some- 
what purified.  They  are  in  the  air,  especially  in 
regions  of  habitation.  Their  numbers  are  great- 
est near  the  surface  of  the  ground,  and  decrease 
in  the  upper  strata  of  air.  Anything  which 
tends  to  raise  dust  increases  the  number  of  bac- 
teria in  the  air  greatly,  and  the  dust  and  emana- 
tions from  the  clothes  of  people  crowded  in  a 
close  room  fill  the  air  with  bacteria  in  very  great 
numbers.  They  are  found  in  excessive  abun- 
dance in  every  bit  of  decaying  matter  wherever  it 
may  be.  Manure  heaps,  dead  bodies  of  animals, 
decaying  trees,  filth  and  slime  and  muck  every- 
where are  filled  with  them,  for  it  is  in  such  places 
that  they  find  their  best  nourishment.  The  bod- 
ies of  animals  contain  them  in  the  mouth,  stom- 
ach, and  intestine  in  great  numbers,  and  this  is,  of 
course,  equally  true  of  man.  On  the  surface  of 
the  body  they  cling  in  great  quantity  ;  attached 
to  the  clothes,  under  the  finger  nails,  among  the 
hairs,  in  every  possible  crevice  or  hiding  place  in 
the  skin,  and  in  all  secretions.  They  do  not, 
however,  occur  in  the  tissues  of  a  healthy  indi- 
vidual, either  in  the  blood,  muscle,  gland,  or  any 
other  organ.  Secretions,  such  as  milk,  urine,  etc., 
always  contain  them,  however,  since  the  bacteria 
do  exist  in  the  ducts  of  the  glands  which  conduct 
the  secretions  to  the  exterior,  and  thus,  while  the 
bacteria  are  never  in  the  healthy  gland  itself, 
they  always  succeed  in  contaminating  the  secre- 
tion as  it  passes  to  the  exterior.  Not  only  higher 
animals,  but  the  lower  animals  also  have  their  bod- 
ies more  or  less  covered  with  bacteria.  Flies  have 
them  on  their  feet,  bees  among  their  hairs,  etc. 


40  THE   STORY  OF  GERM   LIFE. 

In  short,  wherever  on  the  face  of  Nature  there 
is  a  lodging  place  for  dust  there  will  be  found 
bacteria.  In  most  of  these  localities  they  are 
dormant,  or  at  least  growing  only  a  little.  The 
bacteria  clinging  to  the  dry  hair  can  grow  but  lit- 
tle, if  at  all,  and  those  in  pure  water  multiply  very 
little.  When  dried  as  dust  they  are  entirely  dor- 
mant. But  each  individual  bacterium  or  spore 
has  the  potential  power  of  multiplication  already 
noticed,  and  as  soon  as  it  by  accident  falls  upon 
a  place  where  there  is  food  and  moisture  it  will 
begin  to  multiply.  Everywhere  in  Nature,  then, 
exists  this  group  of  organisms  with  its  almost  in- 
conceivable power  of  multiplication,  but  a  power 
held  in  check  by  lack  of  food.  Furnish  them 
with  food  and  their  potential  powers  become 
actual.  Such  food  is  provided  by  the  dead  bod- 
ies of  animals  or  plants,  or  by  animal  secretions, 
or  from  various  other  sources.  The  bacteria  which 
are  fortunate  enough  to  get  furnished  with  such 
food  material  continue  to  feed  upon  it  until  the 
food  supply  is  exhausted  or  their  growth  is 
checked  in  some  other  way.  They  may  be  re- 
garded, therefore,  as  a  constant  and  universal 
power  usually  held  in  check.  With  their  uni- 
versal presence  and  their  powers  of  producing 
chemical  changes  in  food  material,  they  are  ever 
ready  to  produce  changes  in  the  face  of  Nature5 
and  to  these  changes  we  will  now  turn. 


USE  OF  BACTERIA  IN  THE  ARTS.  41 

CHAPTER   II. 

MISCELLANEOUS    USE    OF    BACTERIA   IN    THE   ARTS. 

THE  foods  upon  which  bacteria  live  are  in 
endless  variety,  almost  every  product  of  animal 
or  vegetable  life  serving  to  supply  their  needs. 
Some  species  appear  to  require  somewhat  definite 
kinds  of  food,  and  have  therefore  rather  narrow 
conditions  of  life,  but  the  majority  may  live  upon 
a  great  variety  of  organic  compounds.  As  they 
consume  the  material  which  serves  them  as  food 
they  produce  chemical  changes  therein.  These 
changes  are  largely  of  a  nature  that  the  chemist 
knows  as  decomposition  changes.  By  this  is 
meant  that  the  bacteria,  seizing  hold  of  ingre- 
dients which  constitute  their  food,  break  them  to 
pieces  chemically.  The  molecule  of  the  original 
food  matter  is  split  into  simpler  molecules,  and 
the  food  is  thus  changed  in  its  chemical  nature. 
As  a  result,  the  compounds  which  appear  in  the 
decomposing  solution  are  commonly  simpler  than 
the  original  food  molecules.  Such  products  are 
in  general  called  decomposition  products,  or  some- 
times cleavage  products.  Sometimes,  however,  the 
bacteria  have,  in  addition  to  their  power  of  pull- 
ing their  food  to  pieces,  a  further  power  of  build- 
ing other  compounds  out  of  the  fragments,  thus 
building  up  as  well  as  pulling  down.  But,  how- 
ever they  do  it,  bacteria  when  growing  in  any 
food  material  have  the  power  of  giving  rise  to 
numerous  products  which  did  not  exist  in  the 
food  mass  before.  Because  of  their  extraordi- 
nary powers  of  reproduction  they  are  capable  of 
producing  these  changes  very  rapidly  and  can 


42  THE   STORY  OF  GERM   LIFE. 

give  rise  in  a  short  time  to  large  amounts  of  the 
peculiar  products  of  their  growth. 

It  is  to  these  powers  of  producing  chemical 
changes  in  their  food  that  bacteria  owe  all  their 
importance  in  the  world.  Their  power  of  chem- 
ically destroying  the  food  products  is  in  itself  of 
no  little  importance,  but  the  products  which  arise 
as  the  result  of  this  series  of  chemical  changes 
are  of  an  importance  in  the  world  which  we  are 
only  just  beginning  to  appreciate.  In  our  at- 
tempt to  outline  the  agency  which  bacteria  play 
in  our  industries  and  in  natural  processes  as  well, 
we  shall  notice  that  they  are  sometimes  of  value 
simply  for  their  power  of  producing  decomposi- 
tion ;  but  their  greatest  value  lies  in  the  fact  that 
they  are  important  agents  because  of  the  prod- 
ucts of  their  life. 

We  may  notice,  in  the  first  place,  that  in  the 
arts  there  are  several  industries  which  may  prop- 
erly be  classed  together  as  maceration  industries^ 
all  of  which  are  based  upon  the  decomposition 
powers  of  bacteria.  Hardly  any  animal  or  vege- 
table substance  is  able  to  resist  their  softening 
influence,  and  the  artisan  relies  upon  this  power 
in  several  different  directions. 


BENEFITS    DERIVED    FROM    POWERS    OF 
DECOMPOSITION. 

Linen. — Linen  consists  of  certain  woody  fibres 
of  the  stem  of  the  flax.  The  flax  stem  is  not 
made  up  entirely  of  the  valuable  fibres,  but 
largely  of  more  brittle  wood  fibres,  which  are  of 
no  use.  The  valuable  fibres  are,  however,  close- 
ly united  with  the  wood  and  with  each  other  in 
such  an  intimate  fashion  that  it  is  impossible  to 


USE  OF   BACTERIA  IN  THE  ARTS.  43 

separate  them  by  any  mechanical  means.  The 
whole  cellular  substance  of  the  stem  is  bound 
together  by  some  cementing  materials  which  hold 
it  in  a  compact  mass,  probably  a  salt  of  calcium 
and  pectinic  acid.  The  art  of  preparing  flax  is 
a  process  of  getting  rid  of  the  worthless  wood 
fibres  and  preserving  the  valuable,  longer,  tougher, 
and  more  valuable  fibres,  which  are  then  made 
into  linen.  But  to  separate  them  it  is  necessary 
first  to  soften  the  whole  tissue.  This  is  always 
done  through  the  aid  of  bacteria.  The  flax  stems, 
after  proper  preparation,  are  exposed  to  the  ac- 
tion of  moisture  and  heat,  which  soon  develops  a 
rapid  bacterial  growth.  Sometimes  this  is  done 
by  simply  exposing  the  flax  to  the  dew  and  rain 
and  allowing  it  to  lie  thus  exposed  for  some  time. 
By  another  process  the  stems  are  completely  im- 
mersed in  water  and  allowed  to  remain  for  ten  to 
fourteen  days.  By  a  third  process  the  water  in 
which  the  flax  is  immersed  is  heated  from  75°  to 
90°  F.,  with  the  addition  of  certain  chemicals,  for 
some  fifty  to  sixty  hours.  In  all  cases  the  effect 
is  the  same/  The  moisture  and  the  heat  cause  a 
growth  of  bacteria  which  proceeds  with  more  or 
less  rapidity  according  to  the  temperature  and 
other  conditions.  A  putrefactive  fermentation  is 
thus  set  up  which  softens  the  gummy  substance 
holding  the  fibres  together.  The  process  is  known 
as  "retting,"  and  after  it  is  completed  the  fibres 
are  easily  isolated  from  each  other.  A  purely 
mechanical  process  now  easily  separates  the  valu- 
able fibres  from  the  wood  fibres.  The  whole  pro- 
cess is  a  typical  fermentation.  A  disagreeable 
odour  arises  from  the  fermenting  flax,  and  the 
liquid  after  the  fermentation  is  filled  with  prod- 
ucts which  make  valuable  manure.  The  process 


44  THE  STORY  OF  GERM   LIFE. 

has  not  been  scientifically  studied  until  very  re- 
cently. The  bacillus  which  produces  the  "  ret- 
ting "  is  known  now,  however,  and  it  has  been 
shown  that  the  "  retting  "  is  a  process  of  decom- 
position of  the  pectin  cement.  No  method  of 
separating  the  linen  fibres  in  the  flax  from  the 
wood  fibres  has  yet  been  devised  which  dispenses 
with  the  aid  of  bacteria. 

Jute  and  Hemp. — Almost  exactly  the  same  use 
is  made  of  bacterial  action  in  the  manufacture  of 
jute  and  hemp.  The  commercial  aspect  of  the 
jute  industry  has  grown  to  be  a  large  one,  involv- 
ing many  millions  of  dollars.  Like  linen,  jute  is 
a  fibre  of  the  inner  bark  of  a  plant,  and  is  mixed 
in  the  bark  with  a  mass  of  other  useless  fibrous 
material.  As  in  the  case  of  linen,  a  fermenta- 
tion by  bacteria  is  depended  upon  as  a  means  of 
softening  the  material  so  that  the  fibres  can  be 
disassociated.  The  process  is  called  "  retting," 
as  in  the  linen  manufacture.  The  details  of  the 
process  are  somewhat  different.  The  jute  is  com- 
monly fermented  in  tanks  of  stagnant  water,  al- 
though sometimes  it  is  allowed  to  soak  in  river 
water  for  a  sufficient  length  of  time  to  produce 
the  softening.  After  the  fermentation  is  thus 
started  the  jute  fibre  is  separated  from  the  wood, 
and  is  of  a  sufficient  flexibility  and  toughness  to 
be  woven  into  sacking,  carpets,  curtains,  table 
covers,  and  other  coarse  cloth. 

Practically  the  same  method  is  used  in  sepa- 
rating the  tough  fibres  of  the  hemp.  The  hemp 
plant  contains  some  long  flexible  fibres  with  others 
of  no  value,  and  bacterial  fermentation  is  relied 
upon  to  soften  the  tissues  so  that  they  may  be 
separated. 

Cocoanut  fibre,  a  somewhat  similar  material,  is 


USE  OF  BACTERIA  IN  THE  ARTS.  45 

obtained  from  the  husk  of  the  cocoanut  by  the 
same  means.  The  unripened  husk  is  allowed  to 
steep  and  ferment  in  water  for  a  long  time,  six 
months  or  a  year  being  required.  By  this  time 
the  husk  has  become  so  softened  that  it  can  be 
beaten  until  the  fibres  separate  and  can  be  re- 
moved. They  are  subsequently  made  into  a  num- 
ber of  coarse  articles,  especially  valuable  for  their 
toughness.  Door  mats,  brushes,  ships'  fenders, 
etc.,  are  illustrations  of  the  sort  of  articles  made 
from  them. 

In  each  of  these  processes  the  fermentation 
must  have  a  tendency  to  soften  the  desired  fibres 
as  well  as  the  connecting  substance.  Putrefac- 
tion attacks  all  kinds  of  vegetable  tissue,  and  if 
this  "retting"  continues  too  long  the  desired 
fibre  is  decidedly  injured  by  the  softening  effect 
of  the  fermentation.  It  is  quite  probable  that, 
even  as  commonly  carried  on,  the  fermentation 
has  some  slight  injurious  effect  upon  the  fibre, 
and  that  if  some  purely  mechanical  means  could 
be  devised  for  separating  the  fibre  from  the  wood 
it  would  produce  a  better  material.  But  such 
mechanical  means  has  not  been  devised,  and  at 
present  a  putrefactive  fermentation  appears  to 
be  the  only  practical  method  of  separating  the 
fibres. 

Sponges. — A  somewhat  similar  use  is  made 
of  bacteria  in  the  commercial  preparation  of 
sponges.  The  sponge  of  commerce  is  simply 
the  fibrous  skeleton  of  a  marine  animal.  When 
it  is  alive  this  skeleton  is  completely  filled  with 
the  softer  parts  of  the  animal,  and  to  fit  the 
sponge  for  use  this  softer  organic  material  must 
be  got  rid  of.  It  is  easily  accomplished  by  rot- 
ting. The  fresh  sponges  are  allowed  to  stand  in 


46  THE  STORY  OF  GERM   LIFE. 

the  warm  sun  and  very  rapidly  decay.  Bacteria 
make  their  way  into  the  sponge  and  thoroughly 
decompose  the  soft  tissues.  After  a  short  putre- 
faction of  this  sort  the  softened  organic  matter 
can  be  easily  washed  out  of  the  skeleton  and 
leave  the  clean  fibre  ready  for  market. 

Leather  preparation. — The  tanning  of  leather 
is  a  purely  chemical  process,  and  in  some  pro- 
cesses the  whole  operation  of  preparing  the 
leather  is  a  chemical  one.  In  others,  however; 
especially  in  America,  bacteria  are  brought  into 
action  at  one  stage.  The  dried  hide  which  comes 
to  the  tannery  must  first  have  the  hair  removed 
together  with  the  outer  skin.  The  hide  for  this 
purpose  must  be  moistened  and  softened.  In 
some  tanneries  this  is  done  by  steeping  it  in 
chemicals.  In  others,  however,  it  is  put  into 
water  and  slightly  heated  until  fermentation 
arises.  The  fermentation  softens  it  so  that  the 
outer  skin  can  be  easily  removed  with  a  knife, 
and  the  removal  of  hair  is  accomplished  at  the 
same  time.  Bacterial  putrefaction  in  the  tannery 
is  thus  an  assistance  in  preparing  the  skin  for 
the  tanning  proper.  Even  in  the  subsequent 
tanning  a  bacterial  fermentation  appears  to 
play  a  part,  but  little  is  yet  known  in  regard 
to  it. 

Maceration  of  skeletons. — The  making  of  skele- 
tons for  museums  and  anatomical  instruction  in 
general  is  no  very  great  industry,  and  yet  it  is 
one  of  importance.  In  the  making  of  skeletons 
the  process  of  maceration  is  commonly  used  as 
an  aid.  The  maceration  consists  simply  in  allow- 
ing the  skeleton  to  soak  in  water  for  a  day  or 
two  after  cleaning  away  the  bulk  of  the  muscles. 
The  putrefaction  that  arises  softens  the  connect- 


USE  OF   BACTERIA  IN   THE  ARTS.  47 

ive  tissues  so  much  that  the  bones  may  be  readily 
cleaned  of  flesh. 

Citric  acid. — Bacterial  fermentation  is  em- 
ployed also  in  the  ordinary  preparation  of  citric 
acid.  The  acid  is  made  chiefly  from  the  juice  of 
the  lemon.  The  juice  is  pressed  from  the  fruit 
and  then  allowed  to  ferment.  The  fermentation 
aids  in  separating  a  mucilaginous  mass  and  mak- 
ing it  thus  possible  to  obtain  the  citric  acid  in  a 
purer  condition.  The  action  is  probably  similar 
to  the  maceration  processes  described  above,  al- 
though it  has  not  as  yet  been  studied  by  bacteri- 
ologists. 

BENEFITS   DERIVED    FROM    THE    PRODUCTS    OF 
BACTERIAL    LIFE. 

While  bacteria  thus  play  a  part  in  our  indus- 
tries simply  from  their  power  of  producing  de- 
composition, it  is  primarily  because  of  the  prod- 
ucts of  their  action  that  they  are  of  value. 
Wherever  bacteria  seize  hold  of  organic  matter 
and  feed  upon  it,  there  are  certain  to  be  devel- 
oped new  chemical  compounds,  resulting  largely 
from  decomposition,  but  partly  also  from  con- 
structive processes.  These  new  compounds  are 
of  great  variety.  Different  species  of  bacteria 
do  not  by  any  means  produce  the  same  com- 
pounds even  when  growing  in  and  decomposing 
the  same  food  material.  Moreover,  the  same 
species  of  bacteria  may  give  rise  to  different 
products  when  growing  in  different  food  mate- 
rials. Some  of  the  compounds  produced  by  such 
processes  are  poisonous,  others  are  harmless. 
Some  are  gaseous,  others  are  liquids.  Some 
have  peculiar  odours,  as  may  be  recognised  from 
4 


48  THE   STORY   OF   GERM   LIFE. 

the  smell  arising  from  a  bit  of  decaying  meat. 
Others  have  peculiar  tastes,  as  may  be  realized 
in  the  gamy  taste  of  meat  which  is  in  the  incipi- 
ent stages  of  putrefaction.  By  purely  empirical 
means  mankind  has  learned  methods  of  encourag- 
ing the  development  of  some  of  these  products,  and 
is  to-day  making  practical  use  of  this  power,  pos- 
sessed by  bacteria,  of  furnishing  desired  chemical 
compounds.  Industries  involving  the  investment 
of  hundreds  of  millions  of  dollars  are  founded 
upon  the  products  of  bacterial  life,  and  they  have 
a  far  more  important  relation  to  our  everyday 
life  than  is  commonly  imagined.  In  many  cases 
the  artisan  who  is  dependent  upon  this  action  of 
microscopic  life  is  unaware  of  the  fact.  His 
processes  are  those  which  experience  has  taught 
produce  desired  results,  but,  nevertheless,  his 
dependence  upon  bacteria  is  none  the  less  funda- 
mental. 


BACTERIA    IN    THE    FERMENTATIVE    INDUSTRIES. 

We  may  notice,  first,  several  miscellaneous  in- 
stances of  the  application  of  bacteria  to  various 
fermentative  industries  where  their  aid  is  of  more 
or  less  value  to  man.  In  some  of  the  examples 
to  be  mentioned  the  influence  of  bacteria  is  pro- 
found and  fundamental,  while  in  others  it  is  only 
incidental.  The  fermentative  industries  of  civili- 
zation are  gigantic  in  extent,  and  have  come  to 
be  an  important  factor  in  modern  civilized  life. 
The  large  part  of  the  fermentation  is  based  upon 
the  growth  of  a  class  of  microscopic  plants  which 
we  call  yeasts.  Bacteria  and  yeasts  are  both 
microscopic  plants,  and  perhaps  somewhat  close- 
ly related  to  each  other.  The  botanist  finds  a 


USE  OF  BACTERIA  IN  THE  ARTS.  49 

difference  between  them,  based  upon  their  method 
of  multiplication,  and  therefore  places  them  in 
different  classes  (Fig.  2,  page  19).  In  their  gen- 
eral power  of  producing  chemical  changes  in  their 
food  products,  yeasts  agree  closely  with  bacteria, 
though  the  kinds  of  chemical  changes  are  differ- 
ent. The  whole  of  the  great  fermentative  indus- 
tries, in  which  are  invested  hundreds  of  millions 
of  dollars,  is  based  upon  chemical  decompositions 
produced  by  microscopic  plants.  In  the  great 
part  of  commercial  fermentations  alcohol  is  the 
product  desired,  and  alcohol,  though  it  is  some- 
times produced  by  bacteria,  is  in  commercial 
quantities  produced  only  by  yeasts.  Hence  it  is 
that,  although  the  fermentations  produced  by 
bacteria  are  more  common  in  Nature  than  those 
produced  by  yeasts  and  give  rise  to  a  much  larger 
number  of  decomposition  products,  still  their  com- 
mercial aspect  is  decidedly  less  important  than 
that  of  yeasts.  Nevertheless,  bacteria  are  not 
without  their  importance  in  the  ordinary  ferment- 
ative processes.  Although  they  are  of  no  im- 
portance as  aids  in  the  common  fermentative 
processes,  they  are  not  infrequently  the  cause  of 
much  trouble.  In  the  fermentation  of  malt  to 
produce  beer,  or  grape  juice  to  produce  wine,  it 
is  the  desire  of  the  brewer  and  vintner  to  have 
this  fermentation  produced  by  pure  yeasts,  un- 
mixed with  bacteria.  If  the  yeast  is  pure  the 
fermentation  is  uniform  and  successful.  But  the 
brewer  and  vintner  have  long  known  that  the 
fermentation  is  frequently  interfered  with  by  ir- 
regularities. The  troubles  which  arise  have  long 
been  known,  but  the  bacteriologist  has  finally 
discovered  their  cause,  and  in  general  their  rem- 
edy. The  cause  of  the  chief  troubles  which  arise 


50  THE  STORY  OF  GERM   LIFE. 

in  the  fermentation  is  the  presence  of  contami- 
nating bacteria  among  the  yeasts.  These  bac- 
teria have  been  more  or  less  carefully  studied  by 
bacteriologists,  and  their  effect  upon  the  beer  or 
wine  determined.  Some  of  them  produce  acid 
and  render  the  products  sour ;  others  make  them 
bitter ;  others,  again,  produce  a  slimy  material 
which  makes  the  wine  or  beer  "ropy."  Some- 
thing like  a  score  of  bacteria  species  have  been 
found  liable  to  occur  in  the  fermenting  mate- 
rial and  destroy  the  value  of  the  product  of  both 
the  wine  maker  and  the  beer  brewer.  The  spe- 
cies of  bacteria  which  infect  and  injure  wine  are 
different  from  those  which  infect  and  injure  beer. 
They  are  ever  present  as  possibilities  in  the  great 
alcoholic  fermentations.  They  are  dangers  which 
must  be  guarded  against.  In  former  years  the 
troubles  from  these  sources  were  much  greater 
than  they  are  at  present.  Since  it  has  been  dem- 
onstrated that  the  different  imperfections  in  the 
fermentative  process  are  due  to  bacterial  impuri- 
ties, commonly  in  the  yeasts  which  are  used  to 
produce  the  fermentation,  methods  of  avoiding 
them  are  readily  devised.  To-day  the  vintner 
has  ready  command  of  processes  for  avoiding 
the  troubles  which  arise  from  bacteria,  and  the 
brewer  is  always  provided  with  a  microscope  to 
show  him  the  presence  or  absence  of  the  con- 
taminating bacteria.  While,  then,  the  alcoholic 
fermentations  are  not  dependent  upon  bacteria, 
the  proper  management  of  these  fermentations 
requires  a  knowledge  of  their  habits  and  char- 
acters. 

There  are  certain  other  fermentative  processes 
of  more  or  less  importance  in  their  commercial  as- 
pects, which  are  directly  dependent  upon  bacte- 


USE  OF  BACTERIA  IN  THE  ARTS.  5 1 

rial  action.  Some  of  them  we  should  unhesitat- 
ingly look  upon  as  fermentations,  while  others 
would  hardly  be  thought  of  as  belonging  to  the 
fermentation  industries. 


VINEGAR. 

The  commercial  importance  of  the  manufac- 
ture of  vinegar,  though  large,  does  not,  of  course, 
compare  in  extent  with  that  of  the  alcoholic  fer- 
mentations. Vinegar  is  a  weak  solution  of  acetic 
acid,  together  with  various  other  ingredients 
which  have  come  from  the  materials  furnishing 
the  acid.  In  the  manufacture  of  vinegar,  alcohol 
is  always  used  as  the  source  of  the  acetic  acid. 
The  production  of  acetic  acid  from  alcohol  is  a 
simple  oxidation.  The  equation  C2H6O  +  O2  = 
C2H4O2+H2O  shows  the  chemical  change  that 
occurs.  This  oxidation  can  be  brought  about  by 
purely  chemical  means.  While  alcohol  will  not 
readily  unite  with  oxygen  under  common  condi- 
tions, if  the  alcohol  is  allowed  to  pass  over  a  bit 
of  platinum  sponge  the  union  readily  occurs  and 
acetic  acid  results.  This  method  of  acetic-acid 
production  is  possible  experimentally,  but  is  im- 
practicable on  any  large  scale.  In  the  ordinary 
manufacture  of  vinegar  the  oxidation  is  a  true 
fermentation,  and  brought  about  by  the  growth  of 
bacteria. 

In  the  commercial  manufacture  of  vinegar 
several  different  weak  alcoholic  solutions  are 
used.  The  most  common  of  these  are  fermented 
malt,  weak  wine,  cider,  and  sometimes  a  weak  so- 
lution of  spirit  to  which  is  added  sugar  and  malt. 
If  these  solutions  are  allowed  to  stand  for  a  time 
in  contact  with  air,  they  slowly  turn  sour  by  the 


52  THE  STORY  OF  GERM   LIFE. 

gradual  conversion  of  the  alcohol  into  acetic  acid. 
At  the  close  of  the  process  practically  all  of  the 
alcohol  has  disappeared.  Ordinarily,  however, 
not  all  of  it  has  been  converted  into  acetic  acid, 
for  the  oxidation  does  not  all  stop  at  this  step. 
As  the  oxidation  goes  on,  some  of  the  acid  is 
oxidized  into  carbonic  dioxide,  which  is,  of  course, 
dissipated  at  once  into  the  air,  and  if  the  process 
is  allowed  to  continue  unchecked  for  a  long 
enough  period  much  of  the  acetic  acid  will  be  lost 
in  this  way. 

The  oxidation  of  the  alcohol  in  all  commer- 
cial production  of  vinegar  is  brought  about  by 
the  growth  of  bacteria  in  the  liquid.  When  the 
vinegar  production  is  going  on  properly,  there  is 
formed  on  the  top  of  the  liquid  a  dense  felted  mass 
known  as  the  "  mother  of  vinegar."  This  mass 
proves  to  be  made  of  bacteria  which  have  the 
power  of  absorbing  oxygen  from  the  air,  or,  at  all 
events,  of  causing  the  alcohol  to  unite  with  oxy- 
gen. It  was  at  first  thought  that  a  single  species 
of  bacterium  was  thus  the  cause  of  the  oxidation 
of  alcohol,  and  this  was  named  Mycoderma  aceti. 
But  further  study  ha's  shown  that  several  have 
the  power,  and  that  even  in  the  commercial  man- 
ufacture of  vinegar  several  species  play  a  part 
(Fig.  18),  although  the  different  species  are  not  yet 
very  thoroughly  studied.  Each 'appears  to  act 
best  under  different  conditions.  Some  of  them 
act  slowly,  and  others  rapidly,  the  slow-growing 
species  appearing  to  produce  the  larger  amount 
of  acid  in  the  end.  After  the  amount  of  acetic 
acid  reaches  a  certain  percentage,  the  bacteria  are 
unable  to  produce  more,  even  though  there  be  al- 
cohol still  left  unoxidized.  A  percentage  as  high 
as  fourteen  per  cent,  commonly  destroys  all  their 


USE  OF   BACTERIA  IN  THE  ARTS. 


53 


power  of  growth.  The  production  of  the  acid  is 
wholly  dependent  upon  the  growth  of  the  bacteria, 
and  the  secret  of  the  successful  vinegar  manu- 
facture is  the  skilful  manipulation  of  these  bac- 


FlG.  18. — Bacillus  acettcum,  the  bacterium  which  is  the  common 
cause  of  the  vinegar  fermentation. 

teria  so  as  to  keep  them  in  the  purest  condition 
and  to  give  them  the  best  opportunity  for  growth. 
One  method  of  vinegar  manufacture  which  is 
quite  rapid  is  carried  on  in  a  slightly  different 
manner.  A  tall  cylindrical  chamber  is  filled  with 
wood  shavings,  and  a  weak  solution  of  alcohol  is 
allowed  to  trickle  slowly  through  it.  The  liquid 
after  passing  over  the  shavings  comes  out  after  a 
number  of  hours  well  charged  with  acetic  acid. 
This  process  at  first  sight  appears  to  be  a  purely 
chemical  one,  and  reminds  us  of  the  oxidation 
which  occurs  when  alcohol  is  allowed  to  pass 
over  a  platinum  sponge.  It  has  been  claimed, 
indeed,  that  this  is  a  chemical  oxidation  in  which 
bacteria  play  no  part.  But  this  appears  to  be  an 


54  THE  STORY  OF  GERM   LIFE. 

error.  It  is  always  found  necessary  in  this  method 
to  start  the  process  by  pouring  upon  the  shavings 
some  warm  vinegar.  Unless  in  this  way  the  shav- 
ings become  charged  with  the  vinegar-holding 
bacteria  the  alcohol  will  not  undergo  oxidation 
during  its  passage  over  them,  and  after  the  bac- 
teria thus  introduced  have  grown  enough  to  coat 
the  shavings  .thoroughly  the  acetic-acid  produc- ' 
tion  is  much  more  rapid  than  at  first.  If  vinegar 
is  allowed  to  trickle  slowly  down  a  suspended 
string,  so  that  its  bacteria  may  distribute  them- 
selves through  the  string,  and  then  alcohol  be  al- 
lowed to  trickle  over  it  in  the  same  way,  the  oxida- 
tion takes  place  and  acetic  acid  is  formed.  From 
the  accumulation  of  such  facts  it  has  come  to  be 
recognised  that  all  processes  for  the  commercial 
manufacture  of  vinegar  depend  upon  the  action 
of  bacteria.  While  the  oxidation  of  alcohol  into 
acetic  acid  may  take  place  by  purely  chemical 
means,  these  processes  are  not  practical  on  a  large 
scale,  and  vinegar  manufacturers  everywhere  de- 
pend upon  bacteria  as  their  agents  in  producing 
the  oxidation.  These  bacteria,  several  species  in 
all,  feed  upon  the  nitrogenous  matter  in  the  fer- 
menting mass  and  produce  the  desired  change  in 
the  alcohol. 

This  vinegar  fermentation  is  subject  to  cer- 
tain irregularities,  and  the  vinegar  manufacturers 
can  not  always  depend  upon  its  occurring  in  a 
satisfactory  manner.  Just  as  in  brewing,  so  here, 
contaminating  bacteria  sometimes  find  their  way 
into  the  fermenting  mass  and  interfere  with  its 
normal  course.  In  particular,  the  flavour  of  the 
vinegar  is  liable  to  surfer  from  such  causes.  As 
yet  our  vinegar  manufacturers  have  not  applied 
to  acetic  fermentation  the  same  principle  which 


USE  OF  BACTERIA  IN  THE  ARTS.  55 

has  been  so  successful  in  brewing — namely,  the 
use,  as  a  starter  of  the  fermentation,  of  a  pure  cul- 
ture of  the  proper  species  of  bacteria.  This  has 
been  done  experimentally  and  proves  to  be  feas- 
ible. In  practice,  however,  vinegar  makers  find 
that  simpler  methods  of  obtaining  a  starter — by 
means  of  which  they  procure  a  culture  nearly 
though  not  absolutely  pure — are  perfectly  satis- 
factory. It  is  uncertain  whether  really  pure  cul- 
tures will  ever  be  used  in  this  industry. 

LACTIC  ACID. 

The  manufacture  of  lactic  acid  is  an  industry 
of  less  extent  than  that  of  acetic  acid,  and  yet  it 
is  one  which  has  some  considerable  commercial 
importance.  Lactic  acid  is  used  in  no  large  quan- 
tity, although  it  is  of  some  value  as  a  medicine 
and  in  the  arts.  For  its  production  we  are  wholly 
dependent  upon  bacteria.  It  is  this  acid  which, 
as  we  shall  see,  is  produced  in  the  ordinary 
souring  of  milk,  and  a  large  number  of  species 
of  bacteria  are  capable  of  producing  the  acid 
from  milk  sugar.  Any  sample  of  sour  milk  may 
therefore  always  be  depended  upon  to  contain 
plenty  of  lactic  organisms.  In  its  manufacture 
for  commercial  purposes  milk  is  sometimes  used 
as  a  source,  but  more  commonly  other  substances. 
Sometimes  a  mixture  of  cane  sugar  and  tartaric 
acid  is  used.  To  start  the  fermentation  the  mix- 
ture is  inoculated  with  a  mass  of  sour  milk  or  de- 
caying cheese,  or  both,  such  a  mixture  always  con- 
taining lactic  organisms.  To  be  sure,  it  also 
contains  many  other  bacteria  which  have  differ- 
ent effects,  but  the  acid  producers  are  always  so 
abundant  and  grow  so  vigorously  that  the  lactic 


56  THE  STORY  OF  GERM   LIFE. 

fermentation  occurs  in  spite  of  all  other  bacteria. 
Here  also  there  is  a  possibility  of  an  improve- 
ment in  the  process  by  the  use  of  pure  cultures  of 
lactic  organisms.  Up  to  the  present,  however, 
there  has  been  no  application  of  such  methods. 
The  commercial  aspects  of  the  industry  are  not 
upon  a  sufficiently  large  scale  to  call  for  much  in 
this  direction. 

At  the  present  time  the  only  method  we  have 
for  the  manufacture  of  lactic  acid  is  dependent 
upon  bacteria.  Chemical  processes  for  its  manu- 
facture are  known,  but  not  employed  commer- 
cially. There  are  several  different  kinds  of  lac- 
tic acid.  They  differ  from  each  other  in  the 
relations  of  the  atoms  within  their  molecule,  and 
in  their  relation  to  polarized  light,  some  forms 
rotating  the  plane  of  polarized  light  to  the  right, 
others  to  the  left,  while  others  are  inactive  in  this 
respect.  All  the  types  are  produced  by  fermenta- 
tion processes,  different  species  of  bacteria  hav- 
ing powers  of  producing  the  different  types. 

BUTYRIC    ACID. 

Butyric  acid  is  another  acid  for  which  we  are 
chiefly  dependent  upon  bacteria.  This  acid  is  of 
no  very  great  importance,  and  its  manufacture 
can  hardly  be  called  an  industry ;  still  it  is  to  a 
certain  extent  made,  and  is  an  article  of  commerce. 
It  is  an  acid  that  can  be  manufactured  by  chemical 
means,  but,  as  in  the  case  of  the  last  two  acids,  its 
commercial  manufacture  is  based  upon  bacterial 
action.  Quite  a  number  of  species  of  bacteria 
can  produce  butyric  acid,  and  they  produce  it  from 
a  variety  of  different  sources.  Butyric  acid  is  a 
common  ingredient  in  old  milk  and  in  butter,  and 


THE   USE  OF   BACTERIA  IN   THE  ARTS.         57 

its  formation  by  bacteria  was  historically  one  of 
the  first  bacterial  fermentations  to  be  clearly  un- 
derstood. It  can  be  produced  also  in  various 
sugar  and  starchy  solutions.  Glycerine  may  also 
undergo  a  butyric  fermentation.  The  presence 
of  this  acid  is  occasionally  troublesome,  since  it 
is  one  of  the  factors  in  the  rancidity  of  butter  and 
other  similar  materials. 


INDIGO    PREPARATION. 

The  preparation  of  indigo  from  the  indigo  plant 
is  a  fermentative  process  brought  about  by  a  spe- 
cific bacterium.  The  leaves  of  the  plant  are  im- 
mersed in  water  in  a  large  vat,  and  a  rapid  fer- 
mentation arises.  As  a  result  of  the  fermentation 
the  part  of  the  plant  which  is  the  basis  of  the  in- 
digo is  separated  from  the  leaves  and  dissolved  in 
the  water ;  and  as  a  second  feature  of  the  fer- 
mentation the  soluble  material  is  changed  in  its 
chemical  nature  into  indigo  proper.  As  this 
change  occurs  the  characteristic  blue  colour  is  de- 
veloped, and  the  material  is  rendered  insoluble  in 
water.  It  therefore  makes  its  appearance  as  a 
blue  mass  separated  from  the  water,  and  is  then 
removed  as  indigo. 

Of  the  nature  of  the  process  we  as  yet  know 
very  little.  That  it  is  a  fermentation  is  certain, 
and  it  has  been  proved  that  it  is  produced  by  a 
definite  species  of  bacterium  which  occurs  on  the 
indigo  leaves.  If  the  sterilized  leaves  are  placed 
in  sterile  water  no  fermentation  occurs  and  no 
indigo  is  formed.  If,  however,  some  of  the  spe- 
cific bacteria  are  added  to  the  mass  the  fermenta- 
tion soon  begins  and  the  blue  colour  of  the  indigo 
makes  its  appearance.  It  is  plain,  therefore,  that 


58  THE  STORY  OF  GERM   LIFE. 

indigo  is  a  product  of  bacterial  fermentation,  and 
commonly  due  to  a  single  definite  species  of  bac- 
terium. Of  the  details  of  the  formation,  however, 
we  as  yet  know  little,  and  no  practical  applica- 
tion of  the  facts  have  yet  been  made. 


BACTERIA    IN    TOBACCO    CURING. 

A  fermentative  process  of  quite  a  different  na- 
ture, but  of  immense  commercial  value,  is  found 
in  the  preparation  of  tobacco.  The  process  by 
which  tobacco  is  prepared  is  a  long  and  some- 
what complicated  one,  consisting  of  a  number  of 
different  stages.  The  tobacco,  after  being  first 
dried  in  a  careful  manner,  is  subsequently  allowed 
to  absorb  moisture  from  the  atmosphere,  and  is 
then  placed  in  large  heaps  to  undergo  a  further 
change.  This  process  appears  to  be  a  fermenta- 
tion, for  the  temperature  of  the  mass  rises  rapidly, 
and  every  indication  of  a  fermentative  action  is 
seen.  The  tobacco  in  these  heaps  is  changed 
occasionally,  the  heap  being  thrown  down  and 
built  up  again  in  such  a  way  that  the  portion 
which  was  first  at  the  bottom  comes  to  the  top, 
and  in  this  way  all  parts  of  the  heap  may  be- 
come equally  affected  by  the  process.  After  this 
process  the  tobacco  is  sent  to  the  different  manu- 
facturers, who  finish  the  process  of  curing.  The 
further  treatment  it  receives  varies  widely  ac- 
cording to  the  desired  product,  whether  for  smok- 
ing or  for  snuff,  etc.  In  all  cases,  however, 
fermentations  play  a  prominent  part.  Some- 
times the  leaves  are  directly  inoculated  with  fer- 
menting material.  In  the  preparation  of  snuff 
the  details  of  the  process  are  more  complicated 
than  in  the  preparation  of  smoking  tobacco.  The 


THE  USE  OF  BACTERIA  IN   THE  ARTS.         59 

tobacco,  after  being  ground  and  mixed  with  cer- 
tain ingredients,  is  allowed  to  undergo  a  fermen- 
tation which  lasts  for  weeks,  and  indeed  for 
months.  In  the  different  methods  of  preparing 
snuff  the  fermentations  take  place  in  different 
ways,  and  sometimes  the  tobacco  is  subjected  to 
two  or  three  different  fermentative  actions.  The 
result  of  the  whole  is  the  slow  preparation  of  the 
commercial  product.  It  is  during  the  final  fer- 
mentative processes  that  the  peculiar  colour  and 
flavour  of  the  snuff  are  developed,  and  it  is  during 
the  fermentation  of  the  leaves  of  the  smoking  to- 
bacco— either  the  original  fermentation  or  the 
subsequent  ones — that  the  special  flavours  and 
aromas  of  tobacco  are  produced. 

It  can  not  be  claimed  for  a  moment  that  these 
changes  by  which  the  tobacco  is  cured  and 'finally 
brought  to  a  marketable  condition  are  due  wholly 
to  bacteria.  There  is  no  question  that  chemical 
and  physical  phenomena  play  an  important  part 
in  them.  Nevertheless,  from  the  moment  when 
the  tobacco  is  cut  in  the  fields  until  the  time  it  is 
ready  for  market  the  curing  is  very  intimately 
associated  with  bacteria  and  fermentative  organ- 
isms in  general.  Some  of  these  processes  are 
wholly  brought  about  by  bacterial  life;  in  others 
the  micro-organisms  aid  the  process,  though  they 
perhaps  can  not  be  regarded  as  the  sole  agents. 

At  the  outset  the  tobacco  producer  has  to 
contend  with  a  number  of  micro-organisms  which 
may  produce  diseases  in  his  tobacco.  During  the 
drying  process,  if  the  temperature  or  the  amount 
of  moisture  or  the  access  of  air  is  not  kept  in  a 
proper  condition,  various  troubles  arise  and  va- 
rious diseases  make  their  appearance,  which  either 
injure  or  ruin  the  value  of  the  product.  These 


60  THE  STORY  OF  GERM  LIFE. 

appear  to  be  produced  by  micro-organisms  of 
different  sorts.  During  the  fermentation  which 
follows  the  drying  the  producer  has  to  contend 
with  micro-organisms  that  are  troublesome  to  him  ; 
for  unless  the  phenomena  are  properly  regulated 
the  fermentation  that  occurs  produces  effects 
upon  the  tobacco  which  ruin  its  character.  From 
the  time  the  tobacco  is  cut  until  the  final  stage 
in  the  curing  the  persons  engaged  in  preparing 
it  for  market  must  be  on  a  constant  watch  to 
prevent  the  growth  within  it  of  undesirable  or- 
ganisms. The  preparation  of  tobacco  is  for  this 
reason  a  delicate  operation,  and  one  that  will  be 
very  likely  to  fail  unless  the  greatest  care  is  taken. 
In  the  several  fermentative  processes  which 
occur  in  the  preparation  there  is  no  question  that 
micro-organisms  aid  the  tobacco  producer  and 
manufacturer.  Bacteria  produce  the  first  fermen- 
tation that  follows  the  drying,  and  it  is  these  or- 
ganisms too,  in  large  measure,  that  give  rise  to 
all  the  subsequent  fermentations,  although  seem- 
ingly in  some  cases  purely  chemical  processes 
materially  aid.  Now  the  special  quality  of  the 
tobacco  is  in  part  dependent  upon  the  peculiar 
type  of  fermentation  which  occurs  in  one  or  an- 
other of  these  fermenting  actions.  It  is  the  fer- 
mentation that  gives  rise  to  the  peculiar  flavour 
and  to  the  aroma  of  the  different  grades  of  tobacco. 
Inasmuch  as  the  various  flavours  which  charac- 
terize tobacco  of  different  grades  are  developed, 
at  least  to  a  large  extent,  during  the  fermentation 
processes,  it  is  a  natural  supposition  that  the  dif- 
ferent qualities  of  the  tobacco,  so  far  as  concerns 
flavour,  are  due  to  the  different  types  of  fermen- 
tation. The  number  of  species  of  bacteria  which 
are  found  upon  the  tobacco  leaves  in  the  various 


THE  USE  OF  BACTERIA  IN  THE  ARTS.         6 1 

stages  of  its  preparation  is  quite  large,  and  from 
what  we  have  already  learned  it  is  inevitable  that 
the  different  kinds  of  bacteria  will  produce  dif- 
ferent results  in  the  fermenting  process.  It 
would  seem  natural,  therefore,  to  assume  that  the 
different  flavours  of  different  grades  may  not  un- 
likely be  due  to  the  fact  that  the  tobacco  in  the 
different  cases  has  been  fermented  under  the  in- 
fluence of  different  kinds  of  bacteria. 

Nor  is  this  simply  a  matter  of  inference.  To  a 
certain  extent  experimental  evidence  has  borne  out 
the  conclusion,  and  has  given  at  least  a  slight  in- 
dication of  practical  results  in  the  future.  Acting 
upon  the  suggestion  that  the  difference  between 
the  high  grades  of  tobacco  and  the  poorer  grades 
is  due  to  the  character  of  the  bacteria  that  pro- 
duce the  fermentation,  certain  bacteriologists 
have  attempted  to  obtain  from  a  high  quality  of 
tobacco  the  species  of  bacteria  which  are  infesting 
it.  These  bacteria  have  then  been  cultivated  by 
bacteriological  methods  and  used  in  experiments 
for  the  fermentation  of  tobacco.  If  it  is  true  that 
the  flavour  of  high  grade  tobacco  is  in  large  meas- 
ure, or  even  in  part,  due  to  the  action  of  the  pe- 
culiar microbes  from  the  soil  where  it  grows,  it 
ought  to  be  possible  to  produce  similar  flavours 
in  the  leaves  of  tobacco  grown  in  other  localities, 
if  the  fermentation  of  the  leaves  is  carried  on  by 
means  of  the  pure  cultures  of  bacteria  obtained 
from  the  high  grade  tobacco.  Not  very  much  has 
been  done  or  is  known  in  this  connection  as  yet. 
Two  bacteriologists  have  experimented  independ- 
ently in  fermenting  tobacco  leaves  by  the  action 
of  pure  cultures  of  bacteria  obtained  from  such 
sources.  Each  of  them  reports  successful  experi- 
ments. Each  claims  that  they  have  been  able  to 


62  THE  STORY  OF  GERM   LIFE. 

improve  the  quality  of  tobacco  by  inoculating  the 
leaves  with  a  pure  culture  of  bacteria  obtained 
from  tobacco  having  high  quality  in  flavour.  In 
addition  to  this,  several  other  bacteriologists  have 
carried  on  experiments  sufficient  to  indicate  that 
the  flavours  of  the  tobacco  and  the  character  of 
the  ripening  may  be  decidedly  changed  by  the  use 
of  different  species  of  micro-organisms  in  the  fer- 
mentations that  go  on  during  the  curing  processes. 

In  regard  to  the  whole  matter,  however,  we 
must  recognise  that  as  yet  we  have  very  little 
knowledge.  The  subject  has  been  under  investi- 
gation for  only  a  short  time;  and,  while  consid- 
erable information  has  been  derived,  this  infor- 
mation is  not  thoroughly  understood,  and  our 
knowledge  in  regard  to  the  matter  is  as  yet  in 
rather  a  chaotic  condition.  It  seems  certain, 
however,  that  the  quality  of  tobacco  is  in  large 
measure  dependent  upon  the  character  of  the  fer- 
mentations that  occur  at  different  stages  of  the 
curing.  It  seems  certain  also  that  these  fermen- 
tations are  wholly  or  chiefly  produced  by  micro- 
organisms, and  that  the  character  of  the  fermen- 
tation is  in  large  measure  dependent  upon  the 
species  of  micro-organisms  that  produce  it.  If 
these  are  facts,  it  would  seem  not  improbable 
that  a  further  study  may  produce  practical  re- 
sults for  this  great  industry.  The  study  of  yeasts 
and  the  methods  of  keeping  yeast  from  contami- 
nations has  revolutionised  the  brewing  industry. 
Perhaps  in  this  other  fermentative  industry,  which 
is  of  such  great  commercial  extent,  the  use  of 
pure  cultures  of  bacteria  may  in  the  future  pro- 
duce as  great  revolutions  in  methods  as  it  has  in 
the  industry  of  the  alcoholic  fermentation. 

It  must  not,  however,  be  inferred  that  the  dif- 


THE  USE  OF  BACTERIA  IN  THE  ARTS.         63 

ferences  in  grades  of  tobacco  grown  in  different 
parts  of  the  world  are  due  solely  to  variations  in 
the  curing  processes  and  to  the  types  of  fermen- 
tation. There  are  differences  in  the  texture  of 
the  leaves,  differences  in  the  chemical  composi- 
tion of  the  tobaccoes,  which  are  due  undoubtedly 
to  the  soils  and  the  climatic  conditions  in  which 
they  grow,  and  these,  of  course,  will  never  be  af- 
fected by  changing  the  character  of  the  ferment- 
ative processes.  It  is,  however,  probable  that  in 
so  far  as  the  flavours  that  distinguish  the  high  and 
low  grades  of  tobacco  are  due  to  the  character  of 
the  fermentative  processes,  they  may  be  in  the  fu- 
ture, at  least  to  a  large  extent,  controlled  by  the 
use  of  pure  cultures  in  curing  processes.  Seem- 
ingly, then,  there  is  as  great  a  future  in  the  de- 
velopment of  this  fermentative  industry  as  there 
has  been  in  the  past  in  the  development  of  the 
fermentative  industry  associated  with  brewing 
and  vinting. 

OPIUM. 

Opium  for  smoking  purposes  is  commonly 
allowed  to  undergo  a  curing  process  which  lasts 
several  months.  This  appears  to  be  somewhat 
similar  to  the  curing  of  tobacco.  Apparently  it 
is  a  fermentation  due  to  the  growth  of  micro- 
organisms. The  organisms  in  question  are  not, 
however,  bacteria  in  this  case,  but  a  species  of 
allied  fungus.  The  plant  is  a  mould,  and  it  is 
claimed  that  inoculation  of  the  opium  with  cul- 
tures of  this  mould  hastens  the  curing. 

TROUBLESOME    FERMENTATIONS. 

Before  leaving  this  branch  of  the  subject  it  is 
necessary  to  notice  some  of  the  troublesome  fer- 
5 


64  THE  STORY  OF  GERM   LIFE. 

mentations  which  are  ever  interfering  with  our 
industries,  requiring  special  methods,  or,  indeed, 
sometimes  developing  special  industries  to  meet 
them.  As  agents  of  decomposition,  bacteria  will 
of  course  be  a  trouble  whenever  they  get  into 
material  which  it  is  desired  to  preserve.  Since 
they  are  abundant  everywhere,  it  is  necessary  to 
count  upon  their  attacking  with  certainty  any 
fermentable  substance  which  is  exposed  to  air 
and  water.  Hence  they  are  frequently  the  cause 
of  much  trouble.  In  the  fermentative  industries 
they  occasionally  cause  an  improper  sort  of  fer- 
mentation to  occur  unless  care  is  taken  to  pre- 
vent undesired  species  of  bacteria  from  being 
present.  In  vinegar  making,  improper  species  of 
bacteria  obtaining  access  to  the  solution  give 
rise  to  undesirable  flavours,  greatly  injuring  the 
product.  In  tobacco  curing  it  is  very  common 
for  the  wrong  species  of  bacteria  to  gain  access 
to  the  tobacco  at  some  stage  of  the  curing  and 
by  their  growth  give  rise  to  various  troubles. 
It  is  the  ubiquitous  presence  of  bacteria  which 
makes  it  impossible  to  preserve  fruits,  meats,  or 
vegetables  for  any  length  of  time  without  special 
methods.  This  fact  in  itself  has  caused  the  de- 
velopment of  one  of  our  most  important  indus- 
tries. Canning  meats  or  fruits  consists  in  noth- 
ing more  than  bringing  them  into  a  condition  in 
which  they  will  be  preserved  from  attack  of  these 
micro-organisms.  The  method  is  extremely  sim- 
ple in  theory.  It  is  nothing  more  than  heating 
the  material  to  be  preserved  to  a  high  tempera- 
ture and  then  sealing  it  hermetically  while  it  is 
still  hot.  The  heat  kills  all  the  bacteria  which 
may  chance  to  be  lodged  in  it,  and  the  hermetical 
sealing  prevents  other  bacteria  from  obtaining 


THE  USE   OF   BACTERIA  IN   THE  ARTS.        65 

access.  Inasmuch  as  all  organic  decomposition 
is  produced  by  bacterial  growth,  such  sterilized 
and  sealed  material  will  be  preserved  indefinitely 
when  the  operation  is  performed  carefully  enough. 
The  methods  of  accomplishing  this  with  sufficient 
care  are  somewhat  varied  in  different  industries, 
but  they  are  all  fundamentally  the  same.  It  is 
an  interesting  fact  that  this  method  of  preserving 
meats  was  devised  in  the  last  century,  before  the 
relation  of  micro-organisms  to  fermentation  and 
putrefaction  was  really  suspected.  For  a  long 
time  it  had  been  in  practical  use  while  scientists 
were  still  disputing  whether  putrefaction  could  be 
avoided  by  preventing  the  access  of  bacteria.  The 
industry  has,  however,  developed  wonderfully 
within  the  last  few  years,  since  the  principles 
underlying  it  have  been  understood.  This  un- 
derstanding has  led  to  better  methods  of  destroy- 
ing bacterial  life  and  to  proper  sealing,  and  these 
have  of  course  led  to  greater  success  in  the  pres- 
ervation, until  to-day  the  canning  industries  are 
among  those  which  involve  capital  reckoned  in 
the  millions. 

Occasionally  bacteria  are  of  some  value  in 
food  products.  The  gamy  flavour  of  meats  is 
nothing  more  than  incipient  decomposition. 
Sauer  Kraut  is  a  food  mass  intentionally  allowed 
to  ferment  and  sour.  The  value  of  bacteria  in 
producing  butter  and  cheese  flavours  is  noticed 
elsewhere.  But  commonly  our  aim  must  be  to 
prevent  the  growth  of  bacteria  in  foods.  Foods 
must  be  dried  or  cooked  or  kept  on  ice,  or  some 
other  means  adopted  for  preventing  bacterial 
growth  in  them.  It  is  their  presence  that  forces 
us  to  keep  our  ice  box,  thus  founding  the  ice 
business,  as  well  as  that  of  the  manufacture  of 


66  THE   STORY  OF  GERM   LIFE. 

refrigerators.  It  is  their  presence,  again,  that 
forces  us  to  smoke  hams,  to  salt  mackerel,  to  dry 
fish  or  other  meats,  to  keep  pork  in  brine,  and  to 
introduce  numerous  other  details  in  the  methods 
of  food  preparation  and  preservation. 


CHAPTER   III. 

RELATION    OF    BACTERIA    TO    THE    DAIRY 
INDUSTRY. 

DAIRYING  is  one  of  the  most  primitive  of  our 
industries.  From  the  very  earliest  period,  ever 
since  man  began  to  keep  domestic  cattle,  he  has 
been  familiar  with  dairying.  During  these  many 
centuries  certain  methods  of  procedure  have 
been  developed  which  produce  desired  results. 
These  methods,  however,  have  been  devised  sim- 
ply from  the  accumulation  of  experience,  with 
very  little  knowledge  as  to  the  reasons  underly- 
ing them.  The  methods  of  past  centuries  are, 
however,  ceasing  to  be  satisfactory.  The  ad- 
vance of  our  civilization  during  the  last  half 
century  has  seen  a  marked  expansion  in  the  ex- 
tent of  the  dairy  industry.  With  this  expansion 
has  appeared  the  necessity  for  new  methods,  and 
dairymen  have  for  years  been  looking  for  them. 
The  last  few  years  have  been  teaching  us  that 
the  new  methods  are  to  be  found  along  the  line 
of  the  application  of  the  discoveries  of  modern 
bacteriology.  We  have  been  learning  that  the 
dairyman  is  more  closely  related  to  bacteria  and 
their  activities  than  almost  any  other  class  of 
persons.  Modern  dairying,  apart  from  the  mat- 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.   67 

ter  of  keeping  the  cow,  consists  largely  in  trying 
to  prevent  bacteria  from  growing  in  milk  or  in 
stimulating  their  growth  in  cream,  butter,  and 
cheese.  These  chief  products  of  the  dairy  will  be 
considered  separately. 


SOURCES    OF    BACTERIA    IN    MILK. 

The  first  fact  that  claims  our  attention  is,  that 
milk  at  the  time  it  is  secreted  from  the  udder  of 
the  healthy  cow  contains  no  bacteria.  Although 
bacteria  are  almost  ubiquitous,  they  are  not  found 
in  the  circulating  fluids  of  healthy  animals,  and 
are  not  secreted  by  their  glands.  Milk  when 
first  secreted  by  the  milk  gland  is  therefore  free 
from  bacteria.  It  has  taken  a  long  time  to 
demonstrate  this  fact,  but  it  has  been  finally  satis- 
factorily proved.  Secondly,  it  has  been  demon- 
strated that  practically  all  of  the  normal  changes 
which  occur  in  milk  after  its  secretion  are  caused 
by  the  growth  of  bacteria.  This,  too,  was  long 
denied,  and  for  quite  a  number  of  years  after 
putrefactions  and  fermentations  were  generally 
acknowledged  to  be  caused  by  the  growth  of 
micro-organisms,  the  changes  which  occurred  in 
milk  were  excepted  from  the  rule.  The  uni- 
formity with  which  milk  will  sour,  and  the  diffi- 
culty, or  seeming  impossibility,  of  preventing  this 
change,  led  to  the  belief  that  the  souring  of  milk 
was  a  normal  change  characteristic  of  milk, 
just  as  clotting  is  characteristic  of  blood.  This 
was,  however,  eventually  disproved,  and  it  was 
finally  demonstrated  that,  beyond  a  few  physi- 
cal changes  connected  with  evaporation  and  a 
slight  oxidation  of  the  fat,  milk,  if  kept  free 
from  bacteria,  will  undergo  no  change.  If  bac- 


68  THE  STORY  OF  GERM   LIFE. 

teria  are  not  present,  it  will  remain  sweet  indefi- 
nitely. 

But  it  is  impossible  to  draw  milk  from  the 
cow  in  such  a  manner  that  it  will  be  free  from 
bacteria  except  by  the  use  of  precautions  abso- 
lutely impracticable  in  ordinary  dairying.  As 
milk  is  commonly  drawn,  it  is  sure  to  be  contami- 
nated by  bacteria,  and  by  the  time  it  has  entered 
the  milk  pail  it  contains  frequently  as  many  as 
half  a  million,  or  even  a  million,  bacteria  in  every 
cubic  inch  of  the  milk.  This  seems  almost  in- 
credible, but  it  has  been  demonstrated  in  many 
cases  and  is  beyond  question.  Since  these  bac- 
teria are  not  in  the  secreted  milk,  they  must 
come  from  some  external  sources,  and  these 
sources  are  the  following: 

The  first  in  importance  is  the  cow  herself; 
for  while  her  milk  when  secreted  is  sterile,  and 
while  there  are  no  bacteria  in  her  blood,  neverthe- 
less the  cow  is  the  most  prolific  source  of  bacte- 
rial contamination.  In  the  first  place,  the  milk 
ducts  are  full  of  them.  After  each  milking  a  lit- 
tle milk  is  always  left  in  the  duct,  and  this  fur- 
nishes an  ideal  place  for  bacteria  to  grow.  Some 
bacteria  from  the  air  or  elsewhere  are  sure  to 
get  into  these  ducts  after  the  milking,  and 
they  begin  at  once  to  multiply  rapidly.  By  the 
next  milking  they  become  very  abundant  in  the 
ducts,  and  the  first  milk  drawn  washes  most  of 
them  at  once  into  the  milk  pail,  where  they  can 
continue  their  growth  in  the  milk.  Again,  the 
exterior  of  the  cow's  body  contains  them  in 
abundance.  Every  hair,  every  particle  of  dirt, 
every  bit  of  dried  manure,  is  a  lurking  place  for 
millions  of  bacteria.  The  hind  quarters  of  a 
cow  are  commonly  in  a  condition  of  much  filth, 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.   69 

for  the  farmer  rarely  grooms  his  cow,  and  during 
the  milking,  by  her  movements,  by  the  switching 
of  her  tail,  and  by  the  rubbing  she  gets  from  the 
milker,  no  inconsiderable  amount  of  this  dirt  and 
filth  is  brushed  off  and  falls  into  the  milk  pail. 
The  farmer  understands  this  source  of  dirt  and 
usually  feels  it  necessary  to  strain  the  milk  after 
the  milking.  But  the  straining  it  receives  through 
a  coarse  cloth,  while  it  will  remove  the  coarser 
particles  of  dirt,  has  no  effect  upon  the  bacteria, 
for  these  pass  through  any  strainer  unimpeded. 
Again,  the  milk  vessels  themselves  contain  bac- 
teria, for  they  are  never  washed  absolutely  clean. 
After  the  most  thorough  washing  which  the  milk 
pail  receives  from  the  kitchen,  there  will  always 
be  left  many  bacteria  clinging  in  the  cracks  of  the 
tin  or  in  the  wood,  ready  to  begin  to  grow  as 
soon  as  the  milk  once  more  fills  the  pail.  The 
milker  himself  contributes  to  the  supply,  for  he 
goes  to  the  milking  with  unclean  hands,  unclean 
clothes,  and  not  a  few  bacteria  get  from  him  to 
his  milk  pail.  Lastly,  we  find  the  air  of  the  milk- 
ing stall  furnishing  its  quota  of  milk  bacteria. 
This  source  of  bacteria  is,  however,  not  so  great 
as  was  formerly  believed.  That  the  air  may  con- 
tain many  bacteria  in  its  dust  is  certain,  and 
doubtless  these  fall  in  some  quantity  into  the 
milk,  especially  if  the  cattle  are  allowed  to  feed 
upon  dusty  hay  before  and  during  the  milking. 
But  unless  the  air  is  thus  full  of  dust  this  source 
of  bacteria  is  not  very  great,  and  compared  with 
the  bacteria  from  the  other  sources  the  air  bac- 
teria are  unimportant. 

The  milk  thus  gets  filled  with  bacteria,  and 
since  it  furnishes  an  excellent  food  these  bacteria 
begin  at  once  to  grow.  The  milk  when  drawn  is 


70  THE  STORY  OF  GERM   LIFE. 

warm  and  at  a  temperature  which  especially 
stimulates  bacterial  growth.  They  multiply  with 
great  rapidity,  and  in  the  course  of  a  few  hours 
increase  perhaps  a  thousandfold.  The  numbers 
which  may  be  found  after  twenty-four  hours  are 
sometimes  inconceivable ;  market  milk  may  con- 
tain as  many  as  five  hundred  millions  per  cubic 
inch  ;  and  while  this  is  a  decidedly  extreme  num- 
ber, milk  that  is  a  day  old  will  almost  always 
contain  many  millions  in  each  cubic  inch,  the 
number  depending  upon  the  age  of  the  milk  and 
its  temperature.  During  this  growth  the  bacteria 
have,  of  course,  not  been  without  their  effect. 
Recognising  as  we  do  that  bacteria  are  agents  for 
chemical  change,  we  are  prepared  to  see  the  milk 
undergoing  some  modifications  during  this  rapid 
multiplication  of  bacteria.  The  changes  which 
these  bacteria  produce  in  the  milk  and  its  prod- 
ucts are  numerous,  and  decidedly  affect  its  value. 
They  are  both  advantageous  and  disadvantageous 
to  the  dairyman.  They  are  nuisances  so  far  as 
concerns  the  milk  producer,  but  allies  of  the  but- 
ter and  cheese  maker. 


THE  EFFECT  OF  BACTERIA  ON  MILK. 

The  first  and  most  universal  change  effected 
in  milk  is  its  souring.  So  universal  is  this  phe- 
nomenon that  it  is  generally  regarded  as  an  in- 
evitable change  which  can  not  be  avoided,  and,  as 
already  pointed  out,  has  in  the  past  been  regarded 
as  a  normal  property  of  milk.  To-day,  however, 
the  phenomenon  is  well  understood.  It  is  due  to 
the  action  of  certain  of  the  milk  bacteria  upon 
the  milk  sugar  which  converts  it  into  lactic  acid, 
and  this  acid  gives  the  sour  taste  and  curdles 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.    71 

the  milk.  After  this  acid  is  produced  in  small 
quantity  its  presence  proves  deleterious  to  the 
growth  of  the  bacteria,  and  further  bacterial 
growth  is  checked.  After  souring,  therefore,  the 
milk  for  some  time  does  not  ordinarily  undergo 
any  further  changes. 

Milk  souring  has  been  commonly  regarded  as 
a  single  phenomenon,  alike  in  all  cases.  When  it 
was  first  studied  by  bacteriologists  it  was  thought 
to  be  due  in  all  cases  to  a  single  species  of  micro- 
organism which  was  discovered  to 
be  commonly  present  and  named 
Bacillus  acidi  lactici  (Fig.  19).  This 
bacterium  has  certainly  the  power 
of  souring  milk  rapidly,  and  is 
found  to  be  very  common  in  dai- 
ries in  Europe.  As  soon  as  bacte-  FlG  ^_Bacmus 
riologists  turned  their  attention  acidi  lactici,ft& 
more  closely  to  the  subject  it  was  common  cause 

'  ,      ,      ^  J.  J  of  sour  milk. 

found  that  the  spontaneous  sour- 
ing of  milk  was  not  always  caused  by  the  same 
species  of  bacterium.  Instead  of  finding  this  Ba- 
cillus acidi  lactici  always  present,  they  found  that 
quite  a  number  of  different  species  of  bacteria 
have  the  power  of  souring  milk,  and  are  found  in 
different  specimens  of  soured  milk.  The  number 
of  species  of  bacteria  which  have  been  found  to 
sour  milk  has  increased  until  something  over  a 
hundred  are  known  to  have  this  power.  These 
different  species  do  not  affect  the  milk  in  the 
same  way.  All  produce  some  acid,  but  they 
differ  in  the  kind  and  the  amount  of  acid,  and 
especially  in  the  other  changes  which  are  effected 
at  the  same  time  that  the  milk  is  soured,  so  that 
the  resulting  soured  milk  is  quite  variable.  In 
spite  of  this  variety,,  however,  the  most  .recent 


72  THE   STORY  OF  GERM   LIFE. 

work  tends  to  show  that  the  majority  of  cases  of 
spontaneous  souring  of  milk  are  produced  by 
bacteria  which,  though  somewhat  variable,  prob- 
ably constitute  a  single  species,  and  are  identical 
with  the  Bacillus  acidi  lactici  (Fig.  19).  This  spe- 
cies, found  common  in  the  dairies  of  Europe,  ac- 
cording to  recent  investigations  occurs  in  this 
country  as  well.  We  may  say,  then,  that  while 
there  are  many  species  of  bacteria  infesting  the 
dairy  which  can  sour  the  milk,  there  is  one  which 
is  more  common  and  more  universally  found  than 
others,  and  this  is  the  ordinary  cause  of  milk 
souring. 

When  we  study  more  carefully  the  effect  upon 
the  milk  of  the  different  species  of  bacteria  found 
in  the  dairy,  we  find  that  there  is  a  great  variety 
of  changes  which  they  produce  when  they  are  al- 
lowed to  grow  in  milk.  The  dairyman  expe- 
riences many  troubles  with  his  milk.  It  sometimes 
curdles  without  becoming  acid.  Sometimes  it 
becomes  bitter,  or  acquires  an  unpleasant  "  tainted" 
taste,  or,  again,  a  "soapy"  taste.  Occasionally  a 
dairyman  finds  his  milk  becoming  slimy,  instead  of 
souring  and  curdling  in  the  normal  fashion.  At 
such  times,  after  a  number  of  hours,  the  milk  be- 
comes so  slimy  that  it  can  be  drawn  into  long 
threads.  Such  an  infection  proves  very  trouble- 
some, for  many  a  time  it  persists  in  spite  of  all 
attempts  made  to  remedy  it.  Again,  in  other 
cases  the  milk  will  turn  blue,  acquiring  about  the 
time  it  becomes  sour  a  beautiful  sky-blue  colour. 
Or  it  may  become  red,  or  occasion a\\y  yellow.  All 
of  these  troubles  the  dairyman  owes  to  the  pres- 
ence in  his  milk  of  unusual  species  of  bacteria 
which  grow  there  abundantly. 

Bacteriologists  have  been  able  to  make  out 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.    73 

satisfactorily  the  connection  of  all  these  infec- 
tions with  different  species  of  the  bacteria.  A 
large  number  of  species  have  been  found  to  cur- 
dle milk  without  rendering  it  acid,  several  render 
it  bitter,  and  a  number  produce  a 
"  tainted  "  and  one  a  "  soapy  " 
taste.  A  score  or  more  have  been 
found  which  have  the  power  of 
rendering  the  milk  slimy.  Two 
different  species  at  least  have  the 
power  of  turning  the  milk  to  sky- 
blue  colour;  two  or  three  pro- 
duce  red  pigments  (Fig.  20),  and 
one  or  two  have  been  found  which  produce  a  yel- 
low colour.  In  short,  it  has  been  determined  be- 
yond question  that  all  these  infections,  which  are 
more  or  less  troublesome  to  dairymen,  are  due 
to  the  growth  of  unusual  bacteria  in  the  milk. 

These  various  infections  are  all  troublesome, 
and  indeed  it  may  be  said  that,  so  far  as  concerns 
the  milk  producer  and  the  milk  consumer,  bac- 
teria are  from  beginning  to  end  a  source  of  trou- 
ble. It  is  the  desire  of  the  milk  producer  to 
avoid  them  as  far  as  possible — a  desire  which  is 
shared  also  by  everyone  who  has  anything  to  do 
with  milk  as  milk.  Having  recognised  that  the 
various  troubles,  which  occasionally  occur  even 
in  the  better  class  of  dairies,  are  due  to  bacteria, 
the  dairyman  is,  at  least  in  a  measure,  prepared 
to  avoid  them.  The  avoiding  of  these  troubles 
is  moderately  easy  as  soon  as  dairymen  recog- 
nise the  source  from  which  the  infectious  or- 
ganisms come,  and  also  the  fact  that  low  tem- 
peratures will  in  all  cases  remedy  the  evil  to  a 
large  extent.  With  this  knowledge  in  hand  the 
avoidance  of  all  these  troubles  is  only  a  question 


74  THE  STORY  OF  GERM   LIFE.. 

of  care  in  handling  the  dairy.  It  must  be  recog- 
nised that  most  of  these  troublesome  bacteria 
come  from  some  unusual  sources  of  infection. 
By  unusual  sources  are  meant. those  which  the  ex- 
ercise of  care  will  avoid.  It  is  true  that  the  sour- 
ing; bacteria  appear  to  be  so  universally  distrib- 
uted that  they  can  not  be  avoided  by  any  ordinary 
means.  But  all  other  troublesome  bacteria  .ap- 
pear to  be  within  control.  The  milkman  must 
remember  that  the  sources  of  the  troubles  which 
are  liable  to  arise  in  his  milk  are  in  some  form  of 
filth  :  either  filth  on  the  cow,  or  dust  in  the  hay 
which  is  scattered  through  the  barn,  or  dirt  on 
cows'  udders,  or  some  other  unusual  and  avoid- 
able source.  These  sources,  from  what  we  have 
Already  noticed,  will  always  furnish  the  milk  with 
bacteria;  but  under  common  conditions,  and  when 
the  cow  is  kept  in  conditions  of  ordinary  cleanli- 
ness, and  frequently  even  when  not  cleanly,  will 
only  furnish  bacteria  that  produce  the  universal 
souring.  Recognising  this,  the  dairyman  at  once 
learns  that  his  remedies  for  the  troublesome  in- 
fections are  cleanliness  and  low  temperatures. 
If  he  is  careful  to  keep  his  milk  vessels  scrupu- 
lously clean  ;  if  he  will  keep  his  cow  as  cleanly  as 
he  does  his  horse;  and  if  he  will  use  care  in  and 
around  the  barn  and  dairy,  and  then  apply  low 
temperatures  to  the  milk,  he  need  never  be  dis- 
turbed by  slimy  or  tainted  milk,  or  any  of  these 
other  troubles  ;  or  he  can  remove  such  infections 
speedily  should  they  once  appear.  Pure  sweet 
milk  is  only  a  question  of  sufficient  care.  But 
care  means  labour  and  expense.  As  long  as  we 
'demand  cheap  milk,  so  long  will  we  be  supplied 
with  milk  procured  under  conditions  of  filth.  But 
when  we  learn  that  cheap  milk  is  poor  milk,  and 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.    75 

when  we  are  willing  to  pay  a  little  more  for  it, 
then  only  may  we  expect  the  use  of  greater  care 
in  the  handling  of  the  milk,  resulting  in  a  purer 
product. 

Bacteriology  has  therefore  taught  us  that  the 
whole  question  of  the  milk  supply  in  our  com- 
munities is  one  of  avoiding  the  too  rapid  growth 
of  bacteria.  These  organisms  are  uniformly  a 
nuisance  to  the  milkman.  To  avoid  their  evil 
influence  have  been  designed  all  the  methods  of 
caring  for  the  dairy  and  the  barn,  all  the  methods 
of  distributing  milk  in  ice  cars.  Moreover,  all  the 
special  devices  connected  with  the  great  industry 
of  milk  supply  have  for  their  foundation  the  at- 
tempt to  avoid,  in  the  first  place,  the  presence  of 
too  great  a  number  of  bacteria,  and,  in  the  second 
place,  the  growth  of  these  bacteria. 

BACTERIA    IN    BUTTER    MAKING. 

Cream  ripening. — Passing  from  milk  to  butter, 
we  find  a  somewhat  different  story,  inasmuch  as 
here  bacteria  are  direct  allies  to  the  dairyman 
rather  than  his  enemies.  Without  being  aware  of 
it,  butter  makers  have  for  years  been  making  use 
of  bacteria  in  their  butter  making,  and  have  been 
profiting  by  the  products  which  the  bacteria  have 
furnished  them.  Cream,  as  it  is  obtained  from 
milk,  will  always  contain  bacteria  in  large  quan- 
tity, and  these  bacteria  will  grow  as  readily  in 
the  cream  as  they  will  in  the  milk.  The  butter 
maker  seldom  churns  his  cream  when  it  is  freshly 
obtained  from  the  milk.  There  are,  it  is  true, 
some  places  where  sweet  cream  butter  is  made 
and  is  in  demand,  but  in  the  majority  of  butter- 
consuming  countries  a  different  quality  of  butter 


76  THE  STORY  OF  GERM   LIFE. 

is  desired,  and  the  cream  is  subjected  to  a  process 
known  as  "ripening"  or  "souring"  before  it  is 
churned.  In  ripening,  the  cream  is  simply  al- 
lowed to  stand  in  a  vat  for  a  period  varying 
from  twelve  hours  to  two  or  three  days,  accord- 
ing to  circumstances.  During  this  period  certain 
changes  take  place  therein.  The  bacteria  which 
were  in  the  cream  originally,  get  an  opportunity 
to  grow,  and  by  the  time  the  ripening  is  complete 
they  become  extremely  numerous.  As  a  result, 
the  character  of  the  cream  changes  just  as  the 
milk  is  changed  under  similar  circumstances.  It 
becomes  somewhat  soured;  it  becomes  slightly 
curdled,  and  acquires  a  peculiarly  pleasant  taste 
and  an  aroma  which  was  not  present  in  the  origi- 
nal fresh  cream.  After  this  ripening  the  cream 
is  churned.  It  is  during  the  ripening  that  the 
bacteria  produce  their  effect,  for  after  the  churn- 
ing they  are  of  less  importance.  Part  of  them 
collect  in  the  butter,  part  of  them  are  washed  off 
from  the  butter  in  the  buttermilk  and  the  subse- 
quent processes.  Most  of  the  bacteria  that  are 
left  in  the  butter  soon  die,  not  finding  there  a 
favourable  condition  for  growth  ;  some  of  them, 
however,  live  and  grow  for  some  time  and  are 
prominent  agents  in  the  changes  by  which  butter 
becomes  rancid.  The  butter  maker  is  concerned 
with  the  ripening  rather  than  with  later  processes. 
The  object  of  the  ripening  of  cream  is  to  render 
it  in  a  better  condition  for  butter  making.  The 
butter  maker  has  learned  by  long  experience  that 
ripened  cream  churns  more  rapidly  than  sweet 
cream,  and  that  he  obtains  a  larger  yield  of  butter 
therefrom.  The  great  object  of  the  ripening, 
however,  is  to  develop  in  the  butter  the  peculiar 
flavour  and  aroma  which  is  characteristic  of  the 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.    77 

highest  product.  Sweet  cream  butter  lacks  fla- 
vour and  aroma,  having  indeed  a  taste  almost 
identically  the  same  as  cream.  Butter,  however, 
that  is  made  from  ripened  cream  has  a  peculiar 
delicate  flavour  and  aroma  which  is  well  known  to 
lovers  of  butter,  and  which  is  developed  during 
the  ripening  process. 

Bacteriologists  have  been  able  to  explain  with 
a  considerable  degree  of  accuracy  the  object  of 
this  ripening.  The  process  is  really  a  fermenta- 
tion comparable  to  the  fermentation  that  takes 
place  in  a  brewer's  malt.  The  growth  of  bacteria 
during  the  ripening  produces  chemical  changes 
of  a  somewhat  complicated  character,  and  con- 
cerns each  of  the  ingredients  of  the  milk.  The 
lactic-acid  organisms  affect  the  milk  sugar  and 
produce  lactic  acid ;  others  act  upon  the  fat,  pro- 
ducing slight  changes  therein;  while  others  act 
upon  the  casein  and  the  albumens  of  the  milk. 
As  a  result,  various  biproducts  of  decomposition 
arise,  and  it  is  these  biproducts  of  decomposition 
that  make  the  difference  between  the  ripened  and 
the  unripened  cream.  They  render  it  sour  and 
curdle  it,  and  they  also  produce  the  flavours  and 
aromas  that  characterize  it.  Products  of  decom- 
position are  generally  looked  upon  as  undesirable 
for  food,  and  this  is  equally  true  of  these  products 
that  arise  in  cream  if  the  decomposition  is  allowed 
to  continue  long  enough.  If  the  ripening,  instead 
of  being  stopped  at  the  end  of  a  day  or  two,  is 
allowed  to  continue  several  days,  the  cream  be- 
comes decayed  and  the  butter  made  therefrom  is 
decidedly  offensive.  But  under  the  conditions  of 
ordinary  ripening,  when  the  process  is  stopped  at 
the  right  moment,  the  decomposition  products 
are  pleasant  rather  than  unpleasant,  and  the  fla- 


78  THE  STORY  OF  GERM   LIFE. 

vours  and  aromas  which  they  impart  to  the  cream 
and  to  the  subsequent  butter  are  those  that  are 
desired.  It  is  these  decomposition  products  that 
give  the  peculiar  character  to  a  high  quality  of 
butter,  and  this  peculiar  quality  is  a  matter  that 
determines  the  price  which  the  butter  maker  can 
obtain  for  his  product. 

But,  unfortunately,  the  butter  maker  is  not  al- 
ways able  to  depend  upon  the  ripening.  While 
commonly  it  progresses  in  a  satisfactory  manner, 
sometimes,  for  no  reason  that  he  can  assign,  the 
ripening  does  not  progress  normally.  Instead  of 
developing  the  pleasant  aroma  and  flavour  of  the 
properly  ripened  cream,  the  cream  develops  un- 
pleasant tastes.  It  may  be  bitter  or  somewhat 
tainted,  and  just  as  sure  as  these  flavours  develop 
in  the  cream,  so  sure  does  the  quality  of  the  but- 
ter suffer.  Moreover,  it  has  been  learned  by  ex- 
perience that  some  creameries  are  incapable  of 
obtaining  an  equally  good  ripening  of  their  cream. 
While  some  of  them  will  obtain  favourable  results, 
others,  with  equal  care,  will  obtain  a  far  less  favour- 
able flavour  and  aroma  in  their  butter.  The  rea- 
son for  all  this  has  been  explained  by  modern  bacte- 
riology. In  the  milk,  and  consequently  in  the 
cream,  there  are  always  found  many  bacteria,  but 
these  are  not  always  of  the  same  kinds.  There 
are  scores,  and  probably  hundreds,  of  species  of 
bacteria  common  in  and  around  our  barns  and 
dairies,  and  the  bacteria  that  are  abundant  and 
that  grow  in  different  lots  of  cream  will  not  be 
always  the  same.  It  makes  a  decided  difference 
in  the  character  of  the  ripening,  and  in  the  conse- 
quent flavours  and  aromas,  whether  one  or  another 
species  of  bacteria  has  been  growing  in  the  cream. 
Some  species  are  found  to  produce  good  results 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.    79 

with  desired  flavours,  while  others,  under  identical 
conditions,  produce  decidedly  poor  results  with 
undesired  flavours  (Figs.  21-23).  If  tne  butter 
maker  obtains  cream  which  is  filled  with  a  large 
number  of  bacteria  capable  of  producing  good 
flavours,  then  the  ripening  of  his  cream  will  be 
satisfactory  and  his  butter  will  be  of  high  quality. 
If,  however,  it  chances  that  his  cream  contains 
only  the  species  which  produce  unpleasant  fla- 
vours, then  the  character  of  the  ripening  will  be 
decidedly  inferior  and  the  butter  will  be  of  a 
poorer  grade.  Fortunately  the  majority  of  the 
kinds  of  bacteria  liable  to  get  into  the  cream 
from  ordinary  sources  are  such  as  produce  either 
good  effects  upon  the  cream  or  do  not  materially 
influence  the  flavour  or  aroma.  Hence  it  is  that 
the  ripening  of  cream  will  commonly  produce 
good  results.  Bacteriologists  have  learned  that 
there  are  some  species  of  bacteria  more  or  less 
common  around  our  barns  which  produce  unde- 
sirable effects  upon  flavour,  and  should  these  be- 
come especially  abundant  in  the  cream,  then  the 
character  of  the  ripening  and  the  quality  of  the 
subsequent  butter  will  suffer.  These  malign  spe- 
cies of  bacteria,  however,  are  not  very  common  in 
properly  kept  barns  and  dairies.  Hence  the  pro- 
cess that  is  so  widely  used,  of  simply  allowing 
cream  to  ripen  under  the  influence  of  any  bacte- 
ria that  happen  to  be  in  it,  ordinarily  produces 
good  results.  But  our  butter  makers  sometimes 
find,  at  the  times  when  the  cattle  change  from 
winter  to  summer  or  from  summer  to  winter  feed, 
that  the  ripening  is  abnormal.  The  reason  ap- 
pears to  be  that  the  cream  has  become  infested 
with  an  abundance  of  malign  species.  The  ripen- 
ing that  they  produce  is  therefore  an  undesirable 
6 


80  THE  STORY  OF  GERM   LIFE. 

one,  and  the   quality  of   the   butter   is   sure   to 

suffer. 

So  long  as  butter  was  made  only  in  private 

dairies  it  was   a  matter  of  comparatively  little 

importance  if  there  was  an  occasional  falling  off 
in  quality  of  this  sort.  When 
it  was  made  a  few  pounds 
at  a  time,  and  only  once  or 
twice  a  week,  it  was  not  a 
very  serious  matter  if  a  few 
churnings  of  butter  did  suf- 
fer in  quality.  But  to-day 
the  butter-making  industries 

FIG.  2i.— Dairy  bacterium  are  becoming  more  and  more 

producing    pleasant    fla-    rnnPPnfrptpH         into        larcrp 

vours  in  butter.    This  concentratea  large 

species  has  been  used  creameries,  and  It  IS  a  mat- 
commercially  for  the  rip-  ter  Of  a  good  deal  more  im_ 
enine:  of  cream.  , . 

portance    to   discover  some 

means  by  which  a  uniformly  high  quality  can  be 
insured.  If  a  creamery  which  makes  five  hun- 
dred pounds  of  butter  per  day  suffers  from  such 
an  injurious  ripening,  the  quality  of  its  but- 
ter will  fall  off  to  such  an  extent  as  to  command 
a  lower  price,  and  the  creamery  suffers  material- 
ly. Perhaps  the  continuation  of  such  a  trouble 
for  two  or  three  weeks  would  make  a  difference 
between  financial  success  and  failure  in  the  cream- 
ery. With  our  concentration  of  the  butter-mak- 
ing industries  it  is  becoming  thus  desirable  to 
discover  some  means  of  regulating  this  process 
more  accurately. 

The  remedy  of  these  occasional  ill  effects  in 
cream  ripening  has  not  been  within  the  reach  of 
the  butter  maker.  The  butter  maker  must  make 
butter  with  the  cream  that  is  furnished  him,  and 
if  that  cream  is  already  impregnated  with  malign 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.  8 1 

species  of  bacteria  he  is  helpless.  It  is  true  that 
much  can  be  done  to  remedy  these  difficulties  by 
the  exercise  of  especial  care  in  the  barns  of  the 
patrons  of  the  creamery.  If  the  barns,  the  cows, 
the  dairies,  the  milk  vessels,  etc.,  are  all  kept  in 
condition  of  strict  cleanliness,  if  especial  care  is 
taken  particularly  at  the  seasons 
of  the  year  when  trouble  is  likely 
to  arise,  and  if  some  attention  is 
paid  to  the  kind  of  food  which  the 
cattle  eat,  as  a  rule  the  cream  will 
not  become  infected  with  injurious  FIG.  22.  —  Dairy 
bacteria.  It  may  be  taken  as  a  ^'%££ 
demonstrated  fact  that  these  ma-  aroma  in  butter, 
lign  bacteria  come  from  sources  of 
filth,  and  the  careful  avoidance  of  all  such  sources 
of  filth  will  in  a  very  large  measure  prevent  their 
occurrence  in  the  cream.  Such  measures  as  these 
have  been  found  to  be  practicable  in  many  cream- 
eries. Creameries  which  make  the  highest  priced 
and  the  most  uniform  quality  of  butter  are  those 
in  which  the  greatest  care  is  taken  in  the  barns 
and  dairies  to  insure  cleanliness  and  in  the  han- 
dling of  the  milk  and  cream.  With  such  attention 
a  large  portion  of  the  trouble  which  arises  in  the 
creameries  from  malign  bacteria  may  be  avoided. 
But  these  methods  furnish  no  sure  remedy 
against  evils  of  improper  species  of  bacteria  in 
cream  ripening,  and  do  not  furnish  any  sure 
means  of  obtaining  uniform  flavour  in  butter. 
Even  under  the  very  best  conditions  the  flavour 
of  the  butter  will  vary  with  the  season  of  the 
year.  Butter  made  in  the  winter  is  inferior  to 
that  made  in  the  summer  months  ;  and  while  this 
is  doubtless  due  in  part  to  the  different  food 
which  the  cattle  have  and  to  the  character  of  the 


82  THE  STORY  OF  GERM   LIFE. 

cream  resulting  therefrom,  these  differences  in 
the  flavour  of  the  butter  are  also  in  part  depend- 
ent upon  the  different  species  of  bacteria  which 
are  present  in  the  ripening  of  cream  at  different 
seasons.  The  species  of  bacteria  in  June  cream 
are  different  from  those  that  are  commonly  pres- 
ent in  January  cream,  and  this  is  certainly  a  fac- 
tor in  determining  the  difference  between  winter 
and  summer  butter. 


USE    OF    ARTIFICIAL    BACTERIA    CULTURES    FOR 
CREAM    RIPENING. 

Bacteriologists  have  been  for  some  time  en- 
deavouring to  aid  butter  makers  in  this  direction 
by  furnishing  them  with  the  bacteria  needful  for 
the  best  results  in  cream  ripening.  The  method 
of  doing  this  is  extremely  simple  in  principle,  but 
proves  to  be  somewhat  difficult  in  practice.  It  is 
only  necessary  to  obtain  the  species  of  bacteria 
that  produce  the  highest  results,  and  then  to  fur- 
nish these  in  pure  culture  and  in  large  quantity 
to  the  butter  makers,  to  enable  them  to  inocu- 
late their  cream  with  the  species  of  bacteria 
which  will  produce  the  results  that  they  desire. 
For  this  purpose  bacteriologists  have  been  for 
several  years  searching  for  the  proper  species  of 
bacteria  to  produce  the  best  results,  and  there 
have  been  put  upon  the  market  for  sale  several 
distinct  "pure  cultures  "  for  this  purpose.  These 
have  been  obtained  by  different  bacteriologists 
and  dairymen  in  the  northern  European  countries 
and  also  in  the  United  States.  These  pure  cul- 
tures are  furnished  to  the  dairymen  in  various 
forms,  but  they  always  consist  of  great  quanti- 
ties of  certain  kinds  of  bacteria  which  experience 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.    83 

has  found  to  be  advantageous  for  the  purpose  of 
cream  ripening  (Figs.  21-23). 

There  have  hitherto  appeared  a  number  of 
difficulties  in  the  way  of  reaching  complete  suc- 
cess in  these  directions.  The  most  prominent 
arises  in  devising  a  method  of 
using  pure  cultures  in  the 
creamery.  The  cream  which 
the  butter  makers  desire  to 
ripen  is,  as  we  have  seen,  al- 
ready impregnated  with  bac- 
teria, and  would  ripen  in  a 
fashion  of  its  own  even  if  no 
pure  culture  of  bacteria  were  FlG-  23.— Dairy  bacteri- 
added  thereto.  Pure  cultures  ^fSSSfMS!: 
can  not  therefore  be  used  as 
simply  as  can  yeast  in  bread  dough.  It  is  plain 
that  the  simple  addition  of  a  pure  culture  to  a  mass 
of  cream  would  not  produce  the  desired  effects, 
because  the  cream  would  be  ripened  then,  not  by 
the  pure  culture  alone,  but  by  the  pure  culture 
plus  all  of  the  bacteria  that  were  originally  pres- 
ent. It  would,  of  course,  be  something  of  a  ques- 
tion as  to  whether  under  these  conditions  the 
results  would  be  favourable,  and  it  would  seem 
that  this  method  would  not  furnish  any  means  of 
getting  rid  of  bad  tastes  and  flavours  which  have 
come  from  the  presence  of  malign  species  of  bac- 
teria. It  is  plainly  desirable  to  get  rid  of  the 
cream  bacteria  before  the  pure  culture  is  added. 
This  can  be  readily  done  by  heating  it  to  a  tem- 
perature of  69°  C.  (155°  F.)  for  a  short  time,  this 
temperature  being  sufficient  to  destroy  most  of 
the  bacteria.  The  subsequent  addition  of  the 
pure  culture  of  cream-ripening  bacteria  will  cause 
the  cream  to  ripen  under  the  influence  of  the  add- 


84  THE   STORY  OF  GERM   LIFE. 

ed  culture  alone.  This  method  proves  to  be  suc- 
cessful, and  in  the  butter-making  countries  in 
Europe  it  is  becoming  rapidly  adopted. 

In  this  country,  however,  this  process  has 
not  as  yet  become  very  popular,  inasmuch  as  the 
heating  of  the  cream  is  a  matter  of  considerable 
expense  and  trouble,  and  our  butter  makers  have 
not  been  very  ready  to  adopt  it.  For  this  reason, 
and  also  for  the  purpose  of  familiarizing  butter 
makers  with  the  use  of  pure  cultures,  it  has  been 
attempted  to  produce  somewhat  similar  though 
less  uniform  results  by  the  use  of  pure  cultures 
in  cream  without  previous  healing.  In  the  use 
of  pure  cultures  in  this  way,  the  butter  maker  is 
directed  to  add  to  his  cream  a  large  amount  of 
a  prepared  culture  of  certain  species  of  bacteria, 
upon  the  principle  that  the  addition  of  such  a 
large  number  of  bacteria  to  the  cream,  even 
though  the  cream  is  already  inoculated  with 
certain  bacteria,  will  .produce  a  ripening  of  the 
cream  chiefly  influenced  by  the  artificially  added 
culture.  The  culture  thus  added,  being  present 
in  very  much  greater  quantity  than  the  other 
"wild"  species,  will  have  a  much  greater  effect 
than  any  of  them.  This  method,  of  course,  can- 
not insure  uniformity.  While  it  may  work  satis- 
factorily in  many  cases,  it  is  very  evident  that  in 
others,  when  the  cream  is  already  filled  with  a 
large  number  of  malign  species  of  bacteria,  such 
an  artificial  culture  would  not  produce  the  desired 
results.  This  appears  to  be  not  only  the  theo- 
retical but  the  actual  experience,  The  addition 
of  such  pure  cultures  in  many  cases  produces 
favourable  results,  but  it  does  not  always  do  so, 
and  the  result  is  not  uniform.  While  the  use  of 
pure  cultures  in  this  way  is  an  advantage  over 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.    85 

the  method  of  simply  allowing  the  cream  to  ripen 
normally  without  such  additions,  it  is  a  method 
that  is  decidedly  inferior  to  that  which  first 
pasteurizes  the  cream  and  subsequently  adds  a 
starter. 

There  is  still  another  method  of  adding  bac- 
teria to  cream  to  insure  a  more  advantageous 
ripening,  which  is  frequently  used,  and,  being 
simpler,  is  in  many  cases  a  decided  advantage. 
This  method  is  by  the  use  of  what  is  called  a 
natural  starter.  A  natural  starter  consists  simply 
of  a  lot  of  cream  which  has  been  taken  from  the 
most  favourable  source  possible — that  is,  from 
the  cleanest  and  best  dairy,  or  from  the  herd 
producing  the  best  quality  of  cream — and  allow- 
ing this  cream  to  stand  in  a  warm  place  for  a 
couple  of  days  until  it  becomes  sour.  The  cream 
will  by  that  time  be  filled  with  large  numbers  of 
bacteria,  and  this  is  then  put  as  a  starter  into  the 
vat  of  cream  to  be  ripened.  Of  course,  in  the  use 
of  this  method  the  butter  maker  has  no  control 
over  the  kinds  of  bacteria  that  will  grow  in  the 
starter,  but  it  is  found,  practically,  that  if  the 
cream  is  taken  from  a  good  source  the  results 
are  extremely  favourable,  and  there  is  produced 
in  this  way  almost  always  an  improvement  in  the 
butter. 

The  use  of  pure  cultures  is  still  quite  new, 
particularly  in  this  country.  In  the  European 
butter-making  countries  they  have  been  used  for 
a  longer  period  and  have  become  very  much  bet- 
ter known.  What  the  future  may  develop  along 
this  line  it  is  difficult  to  say ;  but  it  seems  at 
least  probable  that  as  the  difficulties  in  the  de- 
tails are  mastered  the  time  will  come  when  start- 
ers will  be  used  by  our  butter  makers  for  their 


86  THE   STORY  OF  GERM   LIFE. 

cream  ripening,  just  as  yeast  is  used  by  house- 
wives for  raising  bread,  or  by  brewers  for  fer- 
menting malt.  These  starters  will  probably  in 
time  be  furnished  by  bacteriologists.  Bacteriol- 
ogy, in  other  words,  is  offering  in  the  near  future 
to  our  butter  makers  a  method  of  controlling  the 
ripening  of  the  cream  in  such  a  way  as  to  insure 
the  obtaining  of  a  high  and  uniform  quality  of 
butter,  so  far,  at  least,  as  concerns  flavour  and 
aroma. 

BACTERIA    IN    CHEESE. 

Cheese  ripening. — The  third  great  product  of 
the  dairy  industry  is  cheese,  and  in  connection 
with  this  product  the  dairyman  is  even  more  de- 
pendent upon  bacteria  than  he  is  in  the  produc- 
tion of  butter.  In  the  manufacture  of  cheese  the 
casein  of  the  milk  is  separated  from  the  other 
products  by  the  use  of  rennet,  and  is  collected 
in  large  masses  and  pressed,  forming  the  fresh 
cheese.  This  cheese  is  then  set  aside  for  sev- 
eral weeks,  and  sometimes  for  months,  to  under- 
go a  process  that  is  known  as  ripening.  During 
the  ripening  there  are  developed  in  the  cheese  the 
peculiar  flavours  which  are  characteristic  of  the 
completed  product.  The  taste  of  freshly  made 
cheese  is  extremely  unlike  that  of  the  ripened 
product.  While  butter  made  from  unripened 
cream  has  a  pleasant  flavour,  and  one  which  is 
in  many  places  particularly  enjoyed,  there  is  no- 
where a  demand  for  unripened  cheese,  for  the 
freshly  made  cheese  has  a  taste  that  scarce  any 
one  regards  as  pleasant.  Indeed,  the  whole  value 
of  the  cheese  is  dependent  upon  the  flavour  of 
the  product,  and  this  flavour  is  developed  during 
the  ripening. 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.    87 

The  cheese  maker  finds  in  the  ripening  of  his 
cheese  the  most  difficult  part  of  his  manufacture. 
It  is  indeed  a  process  over  which  he  has  very 
little  control.  Even  when  all  conditions  seem  to 
be  correct,  when  cheese  is  made  in  the  most  care- 
ful manner,  it  not  infrequently  occurs  that  the 
ripening  takes  place  in  a  manner  that  is  entire- 
ly abnormal,  and  the  resulting  cheese  becomes 
worthless.  The  cheese  maker  has  been  at  an  en- 
tire loss  to  understand  these  irregularities,  noi 
has  he  possessed  any  means  of  removing  them 
The  abnormal  ripening  that  occurs  takes  on  vari- 
ous types.  Sometimes  the  cheese  will  become 
extraordinarily  porous,  filled  with  large  holes 
which  cause  the  cheese  to  swell  out  of  proper 
shape  and  become  worthless.  At  other  times 
various  spots  of  red  or  blue  appear  in  the  manu- 
factured cheese ;  while  again  unpleasant  tastes 
and  flavours  develop  which  render  the  product  of 
no  value.  Sometimes  a  considerable  portion  of 
the  product  of  the  cheese  factory  undergoes  such 
irregular  ripening,  and  the  product  for  a  long 
time  will  thus  be  worthless.  If  some  means 
could  be  discovered  of  removing  these  irregu- 
larities it  would  be  a  great  boon  to  the  cheese 
manufacturer ;  and  very  many  attempts  have 
been  made  in  one  way  or  another  to  furnish  the 
cheese  maker  with  some  details  in  the  manufac- 
ture which  will  enable  him  in  a  measure  to  con- 
trol the  ripening. 

The  ripening  of  the  cheese  has  been  subjected 
to  a  large  amount  of  study  on  the  part  of  bac- 
teriologists who  have  been  interested  in  dairy 
products.  That  the  ripening  of  cheese  is  the 
result  of  bacterial  growth  therein  appears  to  be 
probable  from.0  priori  grounds.  Like  the  ripen- 


88  THE  STORY  OF  GERM   LIFE. 

ing  of  cream,  it  is  a  process  that  occurs  some- 
what slowly.  It  is  a  chemical  change  which  is 
accompanied  by  the  destruction  of  proteid  mat- 
ter; it  takes  place  best  at  certain  temperatures, 
and  temperatures  which  we  know  are  favourable 
to  the  growth  of  micro-organisms,  all  of  which 
phenomena  suggest  to  us  the  action  of  bacteria. 
Moreover,  the  flavours  and  the  tastes  that  arise 
have  a  decided  resemblance  in  many  cases  to  the 
decomposition  products  of  bacteria,  strikingly  so 
in  Limburger  cheese.  When  we  come  to  study 
the  matter  of  cheese  ripening  carefully  we  learn 
beyond  question  that  this  a  priori  conclusion  is 
correct.  The  ripening  of  any  cheese  is  depend- 
ent upon  several  different  factors.  The  method 
of  preparation,  the  amount  of  water  left  in  the 
curd,  the  temperature  of  ripening,  and  other  mis- 
cellaneous factors  connected  with  the  mechanical 
process  of  cheese  manufacture,  affect  its  charac- 
ter. But,  in  addition  to  all  these  factors,  there  is 
undoubtedly  another  one,  and  that  is  the  number 
and  the  character  of  the  bacteria  that  chance  to 
be  in  the  curd  when  the  cheese  is  made.  While  it 
is  found  that  cheeses  which  are  treated  by  different 
processes  will  ripen  in  a  different  manner,  it  is  also 
found  that  two  cheeses  which  have  been  made 
under  similar  conditions  and  treated  in  identically 
the  same  way  may  also  ripen  in  a  different  manner, 
so  that  the  resulting  flavour  will  vary.  The  varia- 
tions between  cheeses  thus  made  may  be  slight 
or  they  may  be  considerable,  but  variations  cer- 
tainly do  occur.  Every  one  knows  the  great  dif- 
ference in  flavours  of  different  cheeses,  and  these 
flavours  are  due  in  considerable  measure  to  fac- 
tors other  than  the  simple  mechanical  process  of 
making  the  cheese.  The  general  similarity  of 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.    89 

the  whole  process  to  a  bacterial  fermentation 
leads  us  to  believe  at  the  outset  that  some  of 
the  differences  in  character  are  due  to  different 
kinds  of  bacteria  that  multiply  in  the  cheese  and 
produce  decomposition  therein. 

When  the  matter  comes  to  be  studied  by  bac- 
teriology, the  demonstration  of  this  position  be- 
comes easy.  That  the  ripening  of  cheese  is  due 
to  growth  of  bacteria  is  very  easily  proved  by 
manufacturing  cheeses  from  milk  which  is  de- 
prived of  bacteria.  For  instance,  cheeses  have 
been  made  from  milk  that  has  been  either  ster- 
ilized or  pasteurized — which  processes  destroy 
most  of  the  bacteria  therein — and,  treated  other- 
wise in  a  normal  manner,  are  set  aside  to  ripen. 
These  cheeses  do  not  ripen,  but  remain  for  months 
with  practically  the  same  taste  that  they  had 
originally.  In  other  experiments  the  cheese  has 
been  treated  with  a  small  amount  of  disinfective, 
which  is  sufficient  to  prevent  bacteria  from  grow- 
ing, and  again  ripening  is  found  to  be  absolutely 
prevented.  Furthermore,  if  the  cheese  under  or- 
dinary conditions  is  studied  during  the  ripening 
process,  it  is  found  that  bacteria  are  growing  dur- 
ing the  whole  time.  These  facts  all  taken  to- 
gether plainly  prove  that  the  ripening  of  cheese 
is  a  fermentation  due  to  bacteria.  It  will  be 
noticed,  however,  that  the  conditions  in  the 
cheese  are  not  favourable  for  very  rapid  bac- 
terial growth.  It  is  true  that  there  is  plenty 
of  food  in  the  cheese  for  bacterial  life,  but  the 
cheese  is  not  very  moist;  it  is  extremely  dense, 
being  subjected  in  all  cases  to  more  or  less  pres- 
sure. The  penetration  of  oxygen  into  the  centre 
of  the  mass  must  be  extremely  slight.  The  dens- 
ity, the  lack  of  a  great  amount  of  moisture,  and 


90  THE   STORY   OF  GERM   LIFE. 

the  lack  of  oxygen  furnish  conditions  in  which 
bacteria  will  not  grow  very  rapidly.  The  condi- 
tions are  far  less  favourable  than  those  of  ripen- 
ing cream,  and  the  bacteria  do  not  grow  with 
anything  like  the  rapidity  that  they  grow  in 
cream.  Indeed,  the  growth  of  these  organisms 
during  the  ripening  is  extremely  slow  compared 
to  the  possibilities  of  bacterial  growth  that  we 
have  already  noticed.  Nevertheless,  the  bacteria 
do  multiply  in  the  cheese,  and  as  the  ripening 
goes  on  they  become  more  and  more  abundant, 
although  the  number  fluctuates,  rising  and  falling 
under  different  conditions. 

When  the  attempt  is  made  to  determine  the 
relation  of  the  different  kinds  of  ripening  to  dif- 
ferent kinds  of  bacteria,  it  has  thus  far  met  with 
extremely  little  success.  That  different  flavours 
are  due  to  the  ripening  produced  by  different 
kinds  of  bacteria  would  appear  to  be  almost  cer- 
tain when  we  remember,  as  we  have  already  no- 
ticed, the  different  kinds  of  decomposition  pro- 
duced by  different  species  of  bacteria.  It  would 
seem,  moreover,  that  it  ought  not  to  be  very  diffi- 
cult to  separate  from  the  ripened  cheese  the  bac- 
teria which  are  present,  and  thus  obtain  the  kind 
of  bacteria  necessary  to  produce  the  desired  ripen- 
ing. But  for  some  reason  this  does  not  prove  to 
be  so  easy  in  practice  as  it  seems  to  be  in  theory. 
Many  different  species  of  bacteria  have  been  sep- 
arated from  cheeses.  One  bacteriologist,  studying 
several  cheeses,  separated  about  eighty  different 
species  therefrom,  and  others  have  found  perhaps 
as  many  more  from  different  sources.  More- 
over, experiments  have  been  made  with  a  consid- 
erable number  of  these  different  kinds  of  bacteria 
to  determine  whether  they  are  capable  of  produc- 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.    91 

ing  normal  ripening.  These  experiments  consist 
of  making  cheese  out  of  milk  that  has  been  de- 
prived of  its  bacteria,  and  which  has  been  inocu- 
lated with  large  quantities  of  the  species  in  ques- 
tion. Hitherto  these  experiments  have  not  been 
very  satisfactory.  In  some  cases  the  cheese  ap- 
pears to  ripen  scarcely  at  all ;  in  other  cases  the 
ripening  occurs,  but  the  resulting  cheese  is  of  a 
peculiar  character,  entirely  unlike  the  cheese  that 
it  is  desired  to  imitate.  There  have  been  one  or 
two  experiments  in  recent  times  that  give  a  little 
more  promise  of  success  than  the  earlier  ones,  for 
a  few  species  of  bacteria  have  been  used  in  ripen- 
ing with  what  the  authors  have  thought  to  be 
promising  success.  The  cheese  made  from  the 
milk  artificially  inoculated  with  these  species 
ripens  in  a  satisfactory  manner  and  gives  some 
of  the  character  desired,  though  up  to  the  pres- 
ent time  in  no  case  has  the  typical  normal  ripen- 
ing been  produced  in  any  of  these  experiments. 

But  these  experiments  have  demonstrated  be- 
yond question  that  the  abnormal  ripening  which 
is  common  in  cheese  factories  is  due  to  the  pres- 
ence of  undesirable  species  of  bacteria  in  the  milk. 
Many  of  the. experiments  in  making  cheeses  by 
means  of  artificial  cultures  of  bacteria  have  re- 
sulted in  decidedly  abnormal  cheeses.  Many  of 
the  cheeses  thus  manufactured  have  shown  imper- 
fections in  ripening  which  are  identical  with  those 
actually  occurring  in  -the  cheese  factory.  Sev- 
eral different  species  of  bacteria  have  been  found 
which,  when  artificially  used  thus  for  ripening 
cheese,  will  give  rise  to  the  porosity  and  the  ab- 
normal swelling  of  the  cheese  already  referred  to 
(Fig.  24).  Others  produced  bad  tastes  and  fla- 
vours, and  enough  has  been  done  in  this  line  to 


92  THE  STORY  OF  GERM   LIFE. 

demonstrate  beyond  peradventure  that  the  ab- 
normal ripening  of  cheese  is  due  primarily  to  the 
growth  of  improper  species  therein.  Quite  a  long 
list  of  species  of  bacteria  which  produce  abnormal 
ripening  have  been  isolated 
from  cheeses,  and  have 
been  studied  and  experi- 
mented'with  by  bacteriolo- 
gists. As  a  result  of  this 
study  of  abnormal  ripening, 
there  has  been  suggested  a 
method  of  partially  con- 
FIG.  24.— Dairy  bacterium  trolling  these — remedying 

producing:      -swelled"     them>        The     method     COn- 
cheese.  .    ^        .        .  .  . 

sists  simply  in   testing  the 

fermenting  qualities  of  the  milk  used.  A  small 
sample  of  milk  from  different  dairies  is  allowed  to 
stand  in  the  cheese  factory  by  itself  until  it  un- 
dergoes its  normal  souring.  If  the  fermentation 
or  souring  that  thus  occurs  is  of  a  normal  charac- 
ter, the  milk  is  regarded  as  proper  for  cheese 
making.  But  if  the  fermentation  that  occurs  in 
any  particular  sample  of  milk  is  unusual;  if  an 
extraordinary  amount  of  gas  bubbles  are  pro- 
duced, or  if  unpleasant  smells  and  tastes  arise,  , 
the  sample  is  regarded  as  unfavourable  for  cheese 
making,  and  as  likely  to  produce  abnormal  ripen- 
ing in  the  cheeses.  Milk  from  this  source  would 
therefore  be  excluded  from  the  milk  that  is  to  be 
used  in  cheese  making.  This,  of  course,  is  a  ten- 
tative and  an  unsatisfactory  method  of  control- 
ling the  ripening,  and  yet  it  is  one  of  some  prac- 
tical value  to  cheese  makers.  It  is  the  only 
method  that  has  yet  been  suggested  of  control- 
ling the  ripening. 

Our  bacteriologists,  of  course,  are  quite  con- 


RELATION  OF  BACTERIA  TO  DAIRY  INDUSTRY.   93 

fident  that  in  the  future  more  practical  results 
will  be  obtained  along  this  line  than  in  the  past. 
If  it  is  true  that  cheeses  are  ripened  by  bacteria; 
if  it  is  true  that  different  qualities  in  the  cheese 
are  due  to  the  growth  of  different  species  of  bac- 
teria during  the  ripening,  it  would  seem  to  be 
possible  to  obtain  the  proper  kind  of  bacteria 
and  to  furnish  them  to  the  cheese  maker  for  arti- 
ficially inoculating  his  cheese,  just  as  it  has  been 
possible  to  furnish  artificially  cultivated  yeasts  to 
the  brewer,  and  as  it  has  become  possible  to  fur- 
nish artificially  cultivated  bacteria  to  the  butter 
maker.  We  must,  however,  recognise  this  to  be 
a  matter  for  the  future.  Up  to  the  present  time 
no  practical  results  along  the  lines  of  bacteria 
have  been  obtained  which  our  cheese  manufac- 
turers can  make  use  of  in  the  way  of  controlling 
with  any  accuracy  this  process  of  cheese  ripening. 
Thus  it  will  be  seen  that  in  this  last  dairy 
product  bacteria  play  even  a  more  important  part 
than  in  any  of  the  others.  The  food  value  of 
cheese  is  dependent  upon  the  casein  which  is  pres- 
ent. The  market  price,  however,  is  controlled 
entirely  by  the  flavour,  and  this  flavour  is  a  prod- 
uct of  bacterial  growth.  Upon  the  action  of 
bacteria,  then,  the  cheese  maker  is  absolutely  de- 
pendent; and  when  our  bacteriologists  are  able  in 
the  future  to  investigate  this  matter  further,  it 
seems  to  be  at  least  possible  that  they  may  obtain 
some  means  of  enabling  the  cheese  maker  to  con- 
trol the  ripening  accurately.  Not  only  so,  but 
recognising  the  great  variety  in  the  flavours  of 
cheese,  and  recognising  that  different  kinds  of 
bacteria  undoubtedly  produce  different  kinds  of 
decomposition  products,  it  seems  to  be  at  least 
possible  that  a  time  will  come  when  the  cheese 


94  THE  STORY  OF  GERM   LIFE. 

maker  will  be  able  to  produce  at  will  any  particu- 
larly desired  flavour  in  his  cheese  by  the  addition 
to  it  of  particular  species  of  bacteria,  or  particular 
mixtures  of  species  of  bacteria  which  have  been 
discovered  to  produce  the  desired  effects. 


CHAPTER   IV. 

BACTERIA    IN    NATURAL     PROCESSES. 

AGRICULTURE. 

THUS  far,  in  considering  the  relations  of  bac- 
teria to  mankind,  we  have  taken  into  account  only 
the  arts  and  manufactures,  and  have  found  bac- 
teria playing  no  unimportant  part  in  many  of  the 
industries  of  our  modern  civilized  life.  So  im- 
portant are  they  that  there  is  no  one  who  is  not 
directly  affected  by  them.  There  is  hardly  a  mo- 
ment in  our  life  when  we  are  not  using  some  of 
the  direct  or  indirect  products  of  bacterial  action. 
We  turn  now,  however,  to  the  consideration  of  a 
matter  of  even  more  fundamental  importance ; 
for  when  we  come  to  study  bacteria  in  Nature, 
we  find  that  there  are  certain  natural  processes 
connected  with  the  life  of  animals  and  plants  that 
are  fundamentally  based  upon  their  powers.  Liv- 
ing Nature  appears  limitless,  for  life  processes 
have  been  going  on  in  the  world  through  count- 
less centuries  with  seemingly  unimpaired  vigour. 
At  the  very  bottom  we  find  this  never-ending  ex- 
hibition of  vital  power  dependent  upon  certain 
activities  of  micro-organisms.  So  thoroughly  is 
this  true  that,  as  we  shall  find  after  a  short  con- 
sideration, the  continuance  of  life  upon  the  surface 


BACTERIA   IN   NATURAL   PROCESSES.  95 

of  the  world  would  be  impossible  if  bacterial 
action  were  checked  for  any  considerable  length 
of  time.  The  life  of  the  globe  is,  in  short,  de- 
pendent upon  these  micro-organisms. 


BACTERIA    AS    SCAVENGERS. 

In  the  first  place,  we  may  notice  the  value  of 
these  organisms  simply  as  scavengers,  keeping 
the  surface  of  the  earth  in  the  proper  condition 
for  the  growth  of  animals  and  plants.  A  large 
tree  in  the  forest  dies  and  falls  to  the  ground. 
For  a  while  the  tree  trunk  lies  there  a  massive 
structure,  but  in  the  course  of  months  a  slow 
change  takes  place  in  it.  The  bark  becomes  sof- 
tened and  falls  from  the  wood.  The  wood  also 
becomes  more  or  less  softened ;  it  is  preyed  upon 
then  by  insect  life  ;  its  density  decreases  more 
and  more,  until  finally  it  crumbles  into  a  soft, 
brownish,  powdery  mass,  and  eventually  the 
whole  sinks  into  the  soil,  is  overgrown  by  mosses 
and  other  vegetation,  and  the  tree  trunk  has  dis- 
appeared from  view.  In  the  same  way  the  body 
of  the  dead  animal  undergoes  the  process  of  the 
softening  of  its  tissues  by  decay.  The  softer 
parts  of  the  body  rapidly  dissipate,  and  even  the 
bones  themselves  eventually  are  covered  with  the 
soil  and  disintegrated,  until  in  time  they,  too,  dis- 
appear from  any  visible  existence.  This  whole 
process  is  one  of  decay,  and  the  result  is  that 
the  solid  mass  of  the  body  of  the  tree  or  of  the 
animal  has  been  decomposed.  What  has  become 
of  it  ?  The  answer  holds  the  secret  of  Nature's 
eternal  freshness.  Part  of  it  has  dissipated  into 
the  air  in  the  form  of  gases  and  water  vapour; 
part  of  it  has  changed  its  composition  and  has 
7 


96  THE  STORY  OF  GERM  LIFE. 

become  incorporated  into  the  soil,  the  final  result 
being  that  the  body  of  the  plant  or  animal  disap- 
pears as  such,  and  its  substance  is  converted  into 
gaseous  form,  which  is  dissipated  in  the  air  or  into 
simple  compounds  which  sink  into  the  earth. 

This  whole  process  of  decay  of  organic  life  is 
one  in  which  bacteria  play  the  most  important 
part.  In  the  case  of  the  decomposition  of  the 
woody  matter  of  the  tree  trunk,  the  process  is  be- 
gun by  the  agency  of  moulds,  for  this  group  of 
organisms  alone  appears  to  be  capable  of  attack- 
ing such  hard  woody  structure.  The  later  part 
of  the  decay,  however,  is  largely  carried  on  by 
bacterial  life.  In  the  decomposition  of  the  ani- 
mal tissues,  bacteria  alone  are  the  agents.  Thus 
the  process  by  which  organic  matter  is  dissipated 
into  the  air  or  incorporated  into  the  soil  is  one 
which  is  primarily  presided  over  by  bacterial 
life. 

Viewing  this  matter  in  a  purely  mechanical 
light,  the  importance  of  bacteria  in  thus  acting  as 
scavengers  can  hardly  be  overestimated.  If  we 
think  for  a  moment  of  the  condition  of  the  world 
were  there  no  such  decomposing  agents  to  rid  the 
earth's  surface  of  the  dead  bodies  of  animals  and 
plants,  we  shall  see  that  long  since  the  earth 
would  have  been  uninhabitable.  If  the  dead 
bodies  of  plants  and  animals  of  past  ages  simply 
accumulated  on  the  surface  of  the  ground  with- 
out any  forces  to  reduce  them  into  simple  com- 
pounds for  dissipation,  by  their  very  bulk  they 
would  have  long  since  completely  covered  the 
surface  of  the  earth  so  as  to  afford  no  possible 
room  for  further  growth  of  plants  and  animals. 
In  a  purely  mechanical  way,  then,  bacteria  as  de- 
composition agents  are  necessary  to  keep  the  sur- 


BACTERIA   IN   NATURAL   PROCESSES.  97 

face  of  the  earth  fresh  and  unencumbered  so  that 
life  can  continue. 


BACTERIA    AS    AGENTS    IN    NATURE  S    FOOD 
CYCLE. 

But  the  matter  by  no  means  ends  here.  When 
we  come  to  think  of  it,  it  is  a  matter  of  consider- 
able surprise  that  the  surface  of  the  earth  has 
been  able  to  continue  producing  animals  and 
plants  for  the  many  millions  of  years  during 
which  life  has  been  in  existence.  Plants  and  ani- 
mals both  require  food,  animals  depending  wholly 
upon  plants  therefor.  Plants,  however,  equally 
with  animals,  require  food,  and  although  they  ob- 
tain a  considerable  portion  of  their  food  from  the 
air,  yet  no  inconsiderable  part  of  it  is  obtained 
from  the  soil.  The  question  is  forced  upon  us, 
therefore,  as  to  why  the  soil  has  not  long  since 
become  exhausted  of  food.  How  could  the  soil 
continue  to  support  plants  year  after  year  for 
millions  of  years,  and  yet  remain  as  fertile  as 
ever? 

The  explanation  of  this  phenomenon  is  in  the 
simple  fact  that  the  processes  of  Nature  are  such 
that  the  same  food  is  used  over  and  over  again, 
first  by  the  plant,  then  by  the  animal,  and  then 
again  by  the  plant,  and  there  is  no  necessity  for 
any  end  of  the  process  so  long  as  the  sun  fur- 
nishes energy  to  keep  the  circulation  continuous. 
One  phase  of  this  transference  of  food  from 
animal  to  plant  and  from  plant  to  animal  is 
familiar  to  nearly  every  one.  It  is  a  well-known 
fact  that  animals  in  their  respiration  consume 
oxygen,  but  exhale  it  again  in  combination  with 
carbon  as  carbonic  dioxide.  On  the  other  hand, 


98  THE  STORY  OF   GERM   LIFE. 

plants  in  their  life  consume  the  carbonic  dioxide 
and  exhale  the  oxygen  again  as  free  oxygen. 
Thus  each  of  these  kingdoms  makes  use  of  the 
excreted  product  of  the  other,  and  this  process 
can  go  on  indefinitely,  the  animals  furnishing  our 
atmosphere  with  plenty  of  carbonic  acid  for  plant 
life,  and  the  plants  excreting  into  the  atmosphere 
at  the  same  time  an  abundant  sufficiency  of  oxy- 
gen for  animal  life.  The  oxygen  thus  passes  in 
an  endless  round  from  animal  to  plant  and  from 
plant  to  animal. 

A  similar  cycle  is  true  of  all  the  other  foods 
of  animal  and  plant  life,  though  in  regard  to  the 
others  the  operation  is  more  complex  and  more 
members  are  required  to  complete  the  chain. 
The  transference  of  matter  through  a  series  of 
changes  by  which  it  is  brought  from  a  condition 
in  which  it  is  proper  food  for  plants  back  again 
into  a  condition  when  it  is  once  more  a  proper 
food  for  plants,  is  one  of  the  interesting  dis- 
coveries of  modern  science,  and  one  in  which,  as 
we  shall  see,  bacteria  play  a  most  important  part. 
This  food  cycle  is  illustrated  roughly  by  the 
accompanying  diagram ;  but  in  order  to  under- 
stand it,  an  explanation  of  the  various  steps  in 
this  cycle  is  necessary. 

It  will  be  noticed  that  at  the  bottom  of  the 
circle  represented  in  Fig.  25,  at  A,  are  given 
various  ingredients  which  are  found  in  the  soil 
and  which  form  plant  foods.  Plant  foods,  as 
may  be  seen  there,  are  obtained  partly  from  the 
air  as  carbonic  dioxide  and  water;  but  another 
portion  comes  from  the  soil.  Among  the  soil 
ingredients  the  most  prominent  are  nitrates, 
which  are  the  forms  of  nitrogen  compounds 
most  easily  made  use  of  by  plants  as  a  source  of 


BACTERIA  IN  NATURAL  PROCESSES. 


99 


this  important  element.     It  should  be  stated  also 
that  there  are  other  compounds  in  the  soil  which 


PRODUCTS  OF  ANIMAL  LIFE 

c 


FREE\C 
NITROGE'N  ^ 


TUBERCLE  BACTERIA 
AND  LEGUMES 


A 
SOIL  -  NITRATES 

FIG.  25.— Diagram  illustrating  Nature's  food  cycle. 
Explained  in  the  text. 

furnish  plants  with  part  of  their  food — com- 
pounds containing  potassium,  phosphorus,  and 
some  other  elements.  For  simplicity's  sake, 
however,  these  will  be  left  out  of  consideration. 
Beginning  at  the  bottom  of  the  cycle  (Fig.  25  A), 
plant  life  seizes  the  gases  from  the  air  and  these 
foods  from  the  soil,  and  by  means  of  the  energy 
furnished  it  by  the  sun's  rays  builds  these  simple 
chemical  compounds  into  more  complex  ones. 
This  gives  us  the  second  step,  as  shown  in  Fig. 
25  B,  the  products  of  plant  life.  These  products 


100  THE   STORY  OF  GERM   LIFE. 

of  plant  life  consist  of  such  materials  as  sugar, 
starches,  fats,  and  proteids,  all  of  which  have 
been  manufactured  by  the  plant  from  the  ingre- 
dients furnished  it  from  the  soil  and  air,  and 
through  the  agency  of  the  sun's  rays.  These 
products  of  plant  life  now  form  foods  for  the 
animal  kingdom.  Starches,  fats,  and  proteids  are 
animal  foods,  and  upon  such  complex  bodies 
alone  can  the  animal  kingdom  be  fed.  Animal 
life,  standing  high  up  in  the  circle,  is  not  capable 
of  extracting. its  nutriment  from  the  soil,  but  must 
take  the  more  complex  foods  which  have  been 
manufactured  by  plant  life.  These  complex 
foods  enter  now  into  the  animal  and  take  their 
place  in  the  animal  body.  By  the  animal  activi- 
ties, some  of  the  foods  are  at  once  decomposed 
into  carbonic  acid  and  water,  which,  being  dis- 
sipated into  the  air,  are  brought  back  at  once 
into  the  condition  in  which  they  can  serve  again 
as  plant  food.  This  part  of  the  food  is  thus 
brought  back  again  to  the  bottom  of  the  circle 
(Fig.  25,  dotted  lines).  But  while  it  is  true  that 
animals  do  thus  reduce  some  of  their  foods  to 
the  simple  condition  of  carbonic  acid  and  water, 
this  is  not  true  of  most  of  the  foods  which  con- 
tain nitrogen.  The  nitrogenous  foods  are  as 
necessary  for  the  life  as  the  carbon  foods,  and 
animals  do  not  reduce  their  nitrogenous  foods 
to  the  condition  in  which  plants  can  prey  upon 
them.  While  plants  furnish  them  with  nitroge- 
nous food,  they  can  not  give  it  back  to  the  plants. 
Part  of  the  nitrogenous  foods  animals  build  into 
new  albumins  (Fig.  25  C);  but  a  part  of  them  they 
reduce  at  once  into  a  somewhat  simpler  condition 
known  as  urea.  Urea  is  the  form  in  which  the 
nitrogen  is  commonly  excreted  from  the  animal 


BACTERIA  IN   NATURAL   PROCESSES.          IOI 

body.  But  urea  is  not  a  plant  food;  for  ordinary 
plants  are  entirely  unable  to  make  use  of  it. 
Part  of  the  nitrogen  eaten  by  the  animal  is  stored 
up  in  its  body,  and  thus  the  body  of  the  animal, 
after  it  has  died,  contains  these  nitrogen  com- 
pounds of  high  complexity.  But  plants  are  not 
able  to  use  these  compounds.  A  plant  can  not  be 
fed  upon  muscle  tissue,  nor  upon  fats,  nor  bones, 
for  these  are  compounds  so  complex  that  the  sim- 
ple plant  is  unable  to  use  them  at  all.  So  far, 
then,  in  the  food  cycle  the  compounds  taken  from 
the  soil  have  been  built  up  into  compounds  of 
greater  and  greater  complexity ;  they  have  reached 
the  top  of  this  circle,  and  no  part  of  them,  except 
part  of  the  carbon  and  oxygen,  has  become  re- 
duced again  to  plant  food.  In  order  that  this 
material  should  again  become  capable  of  enter- 
ing into  the  life  of  plants  so  as  to  go  over  the 
circle  again,  it  is  necessary  for  it  to  be  once 
more  reduced  from  its  highly  complex  condition 
into  a  simpler  one. 

Now  come  into  play  these  decomposition 
agencies  which  we  have  been  studying  under  the 
head  of  scavengers.  It  will  be  noticed  that  the 
next  step  in  the  food  cycle  is  taken  by  the  de- 
composition bacteria.  These  organisms,  exist- 
ing, as  we  have  already  seen,  in  the  air,  in  the 
soil,  in  the  water,  and  always  ready  to  seize  hold 
of  any  organic  substance  that  may  furnish  them 
with  food,  feed  upon  the  products  of  animal  life, 
whether  they  are  such  products  as  muscle  tissue, 
or  fat,  or  sugar,  or  whether  they  are  the  excreted 
products  of  animal  life,  such  as  urea,  and  produce 
therein  the  chemical  decomposition  changes  al- 
ready noticed.  As  a  result  of  this  chemical 
decomposition,  the  complex  bodies  are  broken 


102  THE   STORY  OF  GERM   LIFE. 

into  simpler  and  simpler  compounds,  and  the 
final  result  is  a  very  thorough  destruction  of  the 
animal  body  or  the  material  excreted  by  animal 
life,  and  its  reduction  into  forms  simple  enough 
for  plants  to  use  again  as  foods.  Thus  the  bac- 
teria come  in  as  a  necessary  link  to  connect  the 
animal  body,  or  the  excretion  from  the  animal 
body,  with  the  soil  again,  and  therefore  with  that 
part  of  the  circle  in  which  the  material  can  once 
more  serve  as  plant  food. 

But  in  the  decomposition  that  thus  occurs 
through  the  agency  of  the  putrefactive  bacteria 
it  very  commonly  happens  that  some  of  the  food 
material  is  broken  down  into  compounds  too  sim- 
ple for  use  as  plant  food.  As  will  be  seen  by  a 
glance  at  the  diagram  (Fig.  25  D),  a  portion  of  the 
cleavage  products  resulting  from  the  destruction 
of  these  animal  foods  takes  the  form  of  carbonic- 
acid  gas  and  water.  These  ingredients  are  at 
once  in  condition  for  plant  life,  as  shown  by  the 
dotted  lines.  They  pass  off  into  the  air,  and  the 
green  leaves  of  vegetation  everywhere  again 
seize  them,  assimilate  them,  and  use  them  as 
food.  Thus  it  is  that  the  carbon  and  the  oxygen 
have  completed  the  cycle,  and  have  come  back 
again  to  the  position  in  the  circle  where  they 
started.  In  regard  to  the  nitrogen  portion  of  the 
food,  however,  it  very  commonly  happens  that  the 
products  which  arise  as  the  result  of  the  decom- 
position processes  are  not  yet  in  proper  condition 
for  plant  food.  They  are  reduced  into  a  condition 
actually  too  simple  for  the  use  of  plants.  As  a 
result  of  these  putrefactive  changes,  the  nitrogen 
products  of  animal  life  are  broken  frequently 
into  compounds  as  simple  as  ammonia  (NH3),  or 
into  compounds  which  the  chemists  speak  of  as 


BACTERIA  IN  NATURAL  PROCESSES.          103 

nitrites  (Fig.  25  at  D).  Now  these  compounds  are 
not  ordinarily  within  the  reach  of  plant  life.  The 
luxuriant  vegetation  of  the  globe  extracts  its  ni- 
trogen from  the  soil  in  a  form  more  complex  than 
either  of  the  compounds  here  mentioned  ;  for,  as 
we  have  seen,  it  is  nitrates  chiefly  that  furnish 
plants  with  their  nitrogen  food  factor.  But  ni- 
trates contain  considerable  oxygen.  Ammonia, 
which  is  one  of  the  products  of  putrefactive  de- 
composition, contains  no  oxygen,  and  nitrites,  an- 
other factor,  contains  less  oxygen  than  nitrates. 
These  bodies  are  thus  too  simple  for  plants  to 
make  use  of  as  a  source  of  nitrogen.  The  chem- 
ical destruction  of  the  food  material  which  results 
from  the  action  of  the  putrefactive  bacteria  is  too 
thorough,  and  the  nitrogen  foods  are  not  yet  in 
condition  to  be  used  by  plants. 

Now  comes  in  the  agency  of  still  another  class 
of  micro-organisms,  the  existence  of  which  has 
been  demonstrated  to  us  during  the  last  few  years. 
In  the  soil  everywhere,  espe- 
cially in  fertile  soil,  is  a  class 
of  bacteria  which  has  received 
the  name  of  nitrifying  bacteria 
(Fig.  26).  These  organisms 
grow  in  the  soil  and  feed  upon 
the  soil  ingredients.  In  the  FlG-  26.— Soil  bacteria 
course  of  their  life  they  have  3ta£^  *" 
somewhat  the  same  action  upon 
the  simple  nitrogen  cleavage  products  just  men- 
tioned as  we  have  already  noticed  the  vinegar- 
producing  species  have  upon  alcohol,  viz.,  the 
bringing  about  a  union  with  oxygen.  There  are 
apparently  several  different  kinds  of  nitrifying 
bacteria  with  different  powers.  Some  of  them 
cause  an  oxidation  of  the  nitrogen  products  by 


104  THE  STORY  OF  GERM   LIFE. 

means  of  which  the  ammonia  is  united  with  oxy- 
gen and  built  up  into  a  series  of  products  finally 
resulting  in  nitrates  (Fig.  26).  By  the  action  of 
other  species  still  higher  nitrogen  compounds,  in- 
cluding the  nitrites,  are  further  oxidized  and  built 
up  into  the  form  of  nitrates.  Thus  these  nitrify- 
ing organisms  form  the  last  link  in  the  chain  that 
binds  the  animal  kingdom  to  the  vegetable  king- 
dom (Fig.  25  at  4).  For  after  the  nitrifying  or- 
ganisms have  oxidized  nitrogen  cleavage  products, 
the  results  of  the  oxidation  in  the  form  of  nitrates 
or  nitric  acid  are  left  in  the  soil,  and  may  now  be 
seized  upon  by  the  roots  of  plants,  and  begin  once 
more  their  journey  around  the  food  cycle.  In  this 
way  it  will  be  seen  that  while  plants,  by  building 
up  compounds,  form  the  connecting  link  between 
the  soil  and  animal  life,  bacteria  in  the  other  half 
of  the  cycle,  by  reducing  them  again,  give  us  the 
connecting  link  between  animal  life  and  the  soil. 
The  food  cycle  would  be  as  incomplete  without 
the  agency  of  bacterial  life  as  it  would  be  with- 
out the  agency  of  plant  life. 

But  even  yet  the  food  cycle  is  not  complete. 
Some  of  the  processes  of  decomposition  appear 
to  cause  a  portion  of  the  nitrogen  to  fly  out  of 
the  circle  at  a  tangent.  In  the  process  of  de- 
composition which  is  going  on  through  the 
agency  of  micro-organisms,  a  considerable  part 
of  the  nitrogen  is  dissipated  into  the  air  in  the 
form  of  free  nitrogen.  When  a  bit  of  meat  de- 
cays, part  of  the  meat  is,  indeed,  converted  into 
ammonia  or  other  nitrogen  compounds,  but  if  the 
putrefaction  is  allowed  to  go  on,  in  the  end  a 
considerable  portion  of  it  will  be  broken  into 
still  simpler  forms,  and  the  nitrogen  will  finally  be 
dissipated  into  the  air  in  the  form  of  free  nitro- 


BACTERIA  IN  NATURAL  PROCESSES.          105 

gen.  This  dissipation  of  free  nitrogen  into  the 
air  is  going  on  in  the  world  wherever  putrefaction 
takes  place.  Wherever  decomposition  of  nitrogen 
products  occurs  some  free  nitrogen  is  eliminated. 
Now,  this  part  of  the  nitrogen  has  passed  beyond 
the  reach  of  plants,  for  plants  can  not  extract 
free  nitrogen  from  the  air.  In  the  diagram  this  is 
represented  as  a  portion  of  the  material  which, 
through  the  agency  of  the  decomposition  bacte- 
ria, has  been  thrown  out  of  the  cycle  at  a  tan- 
gent (Fig.  25  E).  It  will,  of  course,  be  plain 
from  this  that  the  store  of  nitrogen  food  must  be 
constantly  diminishing.  The  soil  may  have  been 
originally  supplied  with  a  given  quantity  of  nitro- 
gen compound,  but  if  the  decomposition  products 
are  causing  considerable  quantities  of  this  nitro- 
gen to  be  dissipated  in  the  air,  it  plainly  follows 
that  the  total  amount  of  nitrogen  food  upon 
which  the  animal  and  vegetable  kingdoms  can 
depend  is  becoming  constantly  reduced  by  such 
dissipation. 

There  are  still  other  methods  by  which  nitro- 
gen is  being  lost  from  the  food  cycle.  First,  we 
may  notice  that  the  ordinary  processes  of  vegeta- 
tion result  in  a  gradual  draining  of  the  soil  and 
a  throwing  of  its  nitrogen  into  the  ocean.  The 
body  of  any  animal  or  any  plant  that  chances  to 
fall  into  a  brook  or  river  is  eventually  carried  to 
the  sea,  and  the  products  of  its  decomposition 
pass  into  the  ocean  and  are,  of  course,  lost  to  the 
soil.  Now,  while  this  gradual  extraction  of  ni- 
trogen from  the  soil  by  drainage  is  a  slow  one,  it 
is  nevertheless  a  sure  one.  It  is  far  more  rapid 
in  these  years  of  civilized  life  than  in  former 
times,  since  the  products  of  the  soil  are  given  to 
the  city,  and  then  are  thrown  into  its  sewage. 


106  THE  STORY  OF  GERM   LIFE. 

Our  cities,  then,  with  our  present  system  of  dis- 
posing of  sewage,  are  draining  from  the  soil  the 
nitrogen  compounds  and  throwing  them  away. 

In  yet  another  direction  must  it  be  noticed 
that  our  nitrogen  compounds  are  being  lost  to 
plant  life — viz.,  by  the  use  of  various  nitrogen 
compounds  to  form  explosives.  Gunpowder,  ni- 
tre-glycerine, dynamite,  in  fact,  nearly  all  the  ex- 
plosives that  are  used  the  world  over  for  all  sorts 
of  purposes,  are  nitrogen  compounds.  When  they 
are  exploded  the  nitrogen  of  the  compound  is 
dissipated  into  the  air  in  the  form  of  gas,  much 
of  it  in  the  form  of  free  nitrogen.  The  basis 
from  which  explosive  compounds  are  made  con- 
tains nitrogen  in  the  form  in  which  it  can  be  used 
by  plants.  Saltpetre,  for  example,  is  equally 
good  as  a  fertilizer  and  as  a  basis  for  gunpowder. 
The  products  of  the  explosion  are  gases  no 
longer  capable  of  use  by  plants,  and  thus  every 
explosion  of  nitrogen  compounds  aids  in  this 
gradual  dissipation  of  nitrogen  products,  taking 
them  from  the  store  of  plant  foods  and  throwing 
them  away. 

All  of  these  agencies  contribute  to  reduce  the 
amount  of  material  circulating  in  the  food  cycle 
of  Nature,  and  thus  seem  to  tend  inevitably  in 
the  end  toward  a  termination  of  the  processes  of 
life;  for  as  soon  as  the  soil  becomes  exhausted  of 
its  nitrogen  compounds,  so  soon  will  plant  life 
cease  from  lack  of  nutrition,  and  the  disappear- 
ance of  animal  life  will  follow  rapidly.  It  is  this 
loss  of  nitrogen  in  large  measure  that  is  forcing 
our  agriculturists  to  purchase  fertilizers.  The 
last  fifteen  years  have  shown  us,  however,  that 
here  again  we  may  look  upon  our  friends,  the 
bacteria,  as  agents  for  counteracting  this  dissi- 


BACTERIA   IN   NATURAL   PROCESSES.          107 

pating  tendency  in  the  general  processes  of  Na- 
ture. Bacterial  life  in  at  least  two  different  ways 
appears  to  have  the  function  of  reclaiming  from 
the  atmosphere  more  or  less  of  this  dissipated 
free  nitrogen. 

In  the  first  place,  it  has  been  found  in  the 
last  few  years  that  soil  entirely  free  from  all 
common  plants,  but  containing  certain  kinds  of 
bacteria,  if  allowed  to  stand  in  contact  with  the 
air,  will  slowly  but  surely  gain  in  the  amount  of 
nitrogen  compounds  that  it  contains.  These 
nitrogen  compounds  are  plainly  manufactured  by 
the  bacteria  in  the  soil ;  for  unless  the  bacteria  are 
present  they  do  not  accumulate,  and  they  do  ac- 
cumulate inevitably  if  the  bacteria  are  present  in 
the  proper  quantity  and  the  proper  species.  It 
appears  that,  as  a  rule,  this  fixation  of  nitrogen 
is  not  performed  by  any  one  species  of  micro- 
organisms, but  by  two  or  three  of  them  acting 
together.  Certain  combinations  of  bacteria  have 
been  found  which,  when  inoculated  in  the  soH, 
will  bring  about  this  fixation  of  nitrogen,  but  no 
one  of  the  species  is  capable  of  producing  this 
result  alone.  We  do  not  know  to  what  extent 
these  organisms  are  distributed  in  the  soil,  nor 
how  widely  this  nitrogen  fixation  through  bacte- 
rial life  is  going  on.  It  is  only  within  a  short 
time  that  it  has  been  demonstrated  to  exist,  but 
we  must  look  upon  bacteria  in  the  soil  as  one  of 
the  factors  in  reclaiming  from  the  atmosphere  the 
dissipated  free  nitrogen. 

The  second  method  by  which  bacteria  aid  in 
the  reclaiming  of  this  lost  nitrogen  is  by  a  com- 
bined action  of  certain  species  of  bacteria  and 
some  of  the  higher  plants.  Ordinary  green 
plants,  as  already  noted,  are  unable  to  make  use 


108  THE  STORY  OF  GERM   LIFE. 

of  the  free  nitrogen  of  the  atmosphere.  It  was 
found,  however,  some  fifteen  years  ago  that  some 
species  of  plants,  chiefly  the  great  family  of 
legumes,  which  contains  the  pea  plant,  the  bean, 
the  clover,  etc.,  are  able,  when  growing  in  soil 
that  is  poor  in  nitrogen,  to  obtain  nitrogen  from 
some  source  other  than  the  soil  in  which  they 
grow.  A  pea  plant  in  soil  that  contains  no  nitro- 
gen products  and  watered  with  water  that  con- 
tains no  nitrogen,  will,  after  sprouting  and  growing 
for  a  length  of  time,  be  found  to  have  accumu- 
lated a  considerable  quantity  of  fixed  nitrogen  in 
its  tissues.  The  only  source  of  this  nitrogen  has 
been  evidently  from  the  air  which  bathes  the 
leaves  of  the  plant  or  permeates  the  soil  and 
bathes  its  roots.  This  fact 
was  at  first  disputed,  but  sub- 
sequently demonstrated  to  be 
true,  and  was  found  later  to 
be  associated  with  the  com- 
bined action  of  these  legumes 
and  certain  soil  bacteria. 
When  a  legume  thus  gains 
FIG.  27.-Soii  bacteria  nitrogen  from  the  air,  it  de- 

which     produce  tu-    Velops    Upon    its     TOOtS     little 

bercies  on  the  roots  bunches  known  as  root  nod- 
ules or  root  tubercles.  The 
nodules  are  sometimes  the  size  of  the  head  of  a 
pin,  and  sometimes  much  larger  than  this,  occa- 
sionally reaching  the  size  of  a  large  pea,  or  even 
larger.  Upon  microscopic  examination  they 
are  found  to  be  little  nests  of  bacteria.  In  some 
way  the  soil  organisms  (Fig.  27)  make  their  way 
into  the  roots  of  the  sprouting  plant,  and  find- 
ing there  congenial  environment,  develop  in  con- 
siderable quantities  and  produce  root  tubercles 


BACTERIA   IN   NATURAL   PROCESSES.          109 

in  the  root.  Now,  by  some  entirely  unknown 
process,  the  legume  and  the  bacteria  growing  to- 
gether succeed  in  extracting  the  nitrogen  from 
the  atmosphere  which  permeates  the  soil,  and  fix- 
ing this  nitrogen  in  the  tubercles  and  the  roots  in 
the  form  of  nitrogen  compounds.  The  result  is 
that,  after  a  proper  period  of  growth,  the  amount 
of  fixed  nitrogen  in  the  plant  is  found  to  have 
very  decidedly  increased  (Fig.  25  E.). 

This,  of  course,  furnishes  a  starting  point  for 
the  reclaiming  of  the  lost  atmospheric  nitrogen. 
The  legume  continues  to  live  its  usual  life,  per- 
haps increasing  the  store  of  nitrogen  in  its  roots 
and  stems  and  leaves  during  the  whole  of  its 
normal  growth.  Subsequently,  after  having  fin- 
ished its  ordinary  life,  the  plant  will  die,  and  then 
the  roots  and  stems  and  leaves,  falling  upon  the 
ground  and  becoming  buried,  will  be  seized  upon 
by  the  decomposition  bacteria  already  men- 
tioned. The  nitrogen  which  has  thus  become 
fixed  in  their  tissues  will  undergo  the  destructive 
changes  already  described.  This  will  result 
eventually  in  the  production  of  nitrates.  Thus 
some  of  the  lost  nitrogen  is  restored  again  to  the 
soil  in  the  form  of  nitrates,  and  may  now  start 
on  its  route  once  more  around  the  cycle  of  food. 

It  will  be  seen,  then,  that  the  food  cycle  is  a 
complete  one.  Beginning  with  the  mineral  in- 
gredients in  the  soil,  the  food  matter  may  start 
on  its  circulation  from  the  soil  to  the  plant,  from 
the  plant  to  the  animal,  from  the  animal  to  the 
bacterium,  and  from  the  bacterium  through  a 
series  of  other  bacteria  back  again  to  the  soil  in 
the  condition  in  which  it  started.  If,  perchance, 
in  this  progress  around  the  circle  some  of  the 
nitrogen  is  thrown  off  at  a  tangent,  this,  too, 


110  THE  STORY  OF  GERM   LIFE. 

is  brought  back  again  to  the  circle  through 
the  agency  of  bacterial  life.  And  so  the  food 
material  of  animals  and  plants  continues  in  this 
never-ceasing  circulation.  It  is  the  sunlight  that 
furnishes  the  energy  for  the  motion.  It  is  the 
sunlight  that  forces  the  food  around  the  circle 
and  keeps  up  the  endless  change ;  and  so  long  as 
the  sun  continues  to  shine  upon  the  earth  there 
seems  to  be  no  reason  why  the  process  should 
ever  cease.  It  is  this  repeated  circulation  that 
has  made  the  continuation  of  life  possible  for  the 
millions  and  millions  of  years  of  the  earth's  his- 
tory. It  is  this  continued  circulation  that  makes 
life  possible  still,  and  it  is  only  this  fact  that  the 
food  is  thus  capable  of  ever  circulating  from  ani- 
mal to  plant  and  from  plant  to  animal  that  makes 
it  possible  for  the  living  world  to  continue  its 
existence.  But,  as  we  have  seen,  one  half  of  this 
great  circle  of  food  change  is  dependent  upon 
bacterial  life.  Without  the  bacterial  life  the  ani- 
mal body  and  the  animal  excretion  could  never 
be  brought  back  again  within  the  reach  of  the 
plant ;  and  thus,  were  it  not  for  the  action  of 
these  micro-organisms  the  food  cycle  would  be 
incomplete  and  life  could  not  continue  indefi- 
nitely upon  the  surface  of  the  earth.  At  the 
very  foundation,  the  continuation  of  the  present 
condition  of  Nature  and  the  existence  of  life 
during  the  past  history  of  the  world  has  been 
fundamentally  based  upon  the  ubiquitous  pres- 
ence of  bacteria  and  upon  their  continual  action 
in  connection  with  both  destructive  and  con- 
structive processes. 


BACTERIA  IN  NATURAL  PROCESSES.    Ill 
RELATION  OF  BACTERIA  TO  AGRICULTURE. 

We  have  already  noticed  that  bacteria  play 
an  important  part  in  some  of  the  agricultural  in- 
dustries, particularly  in  the  dairy.  From  the 
consideration  of  the  matters  just  discussed,  it  is 
manifest  that  these  organisms  must  have  an  even 
more  intimate  relation  to  the  farmer's  occupation. 
At  the  foundation,  farming  consists  in  the  culti- 
vation of  plants  and  animals,  and  we  have  al- 
ready seen  how  essential  are  the  bacteria  in  the 
continuance  of  animal  and  plant  life.  But  aside 
from  these  theoretical  considerations,  a  little 
study  shows  that  in  a  very  practical  manner  the 
farmer  is  ever  making  use  of  bacteria,  as  a  rule, 
quite  unconsciously,  but  none  the  less  positively. 

SPROUTING    OF    SEEDS. 

Even  in  the  sprouting  of  seeds  after  they  are 
sown  in  the  soil  bacterial  life  has  its  influence. 
When  seeds  are  placed  in  moist  soil  they  germi- 
nate under  the  influence  of  heat.  The  rich  albu- 
minous material  in  the  seeds  furnishes  excellent 
food,  and  inasmuch  as  bacteria  abound  in  the 
soil,  it  is  inevitable  that  they  should  grow  in  and 
feed  upon  the  seed.  If  the  moisture  is  excessive 
and  the  heat  considerable,  they  very  frequently 
grow  so  rapidly  in  the  seed  as  to  destroy  its  life 
as  a  seedling.  The  seed  rots  in  the  ground  as  a 
result.  This  does  not  commonly  occur,  however, 
in  ordinary  soil.  But  even  here  bacteria  do  grow 
in  the  seed,  though  not  so  abundantly  as  to  pro- 
duce any  injury.  Indeed,  it  has  been  claimed 
that  their  presence  in  the  seed  in  small  quantities 
is  a  necessity  for  the  proper  sprouting  of  the 
8 


112  THE   STORY   OF  GERM   LIFE. 

seed.  It  has  been  claimed  that  their  growth  tends 
to  soften  the  food  material  in  the  seed,  so  that 
the  young  seedling  can  more  readily  absorb  it  for 
its  own  food,  and  that  without  such  a  softening 
the  seed  remains  too  hard  for  the  plant  to  use. 
This  may  well  be  doubted,  however,  for  seeds 
can  apparently  sprout  well  enough  without  the 
aid  of  bacteria.  But,  nevertheless,  bacteria  do 
grow  in  the  seed  during  its  germination,  and  thus 
do  aid  the  plant  in  the  softening  of  the  food  ma- 
terial. We  can  not  regard  them  as  essential  to 
seed  germination.  It  may  well  be  claimed  that 
they  ordinarily  play  at  least  an  incidental  part  in 
this  fundamental  life  process,  although  it  is  un- 
certain whether  the  growth  of  seedlings  is  to  any 
considerable  extent  aided  thereby. 

THE  SILO. 

In  the  management  of  a  silo  the  farmer  has 
undoubtedly  another  great  bacteriological  prob- 
lem. In  the  attempt  to  preserve  his  summer- 
grown  food  for  the  winter  use  of  his  animals, 
he  is  hindered  by  the  activity  of  common  bac- 
teria. If  the  food  is  kept  moist,  it  is  sure  to 
undergo  decomposition  and  be  ruined  in  a  short 
time  as  animal  food.  The  farmer  finds  it  neces- 
sary, therefore,  to  dry  some  kinds  of  foods,  like 
hay.  While  he  can  thus  preserve  some  foods, 
others  can  not  be  so  treated.  Much  of  the  rank 
growth  of  the  farm,  like  cornstalks,  is  good  food 
while  it  is  fresh,  but  is  of  little  value  when  dried. 
The  farmer  has  from  experience  and  observation 
discovered  a  method  of  managing  bacterial 
growth  which  enables  him  to  avoid  their  ordinary 
evil  effects.  This  is  by  the  use  of  the  silo.  The 


BACTERIA  IN   NATURAL   PROCESSES.          113 

silo  is  a  large,  heavily  built  box,  which  is  open 
only  at  the  top.  In  the  silo  the  green  food  is 
packed  tightly,  and  when  full  all  access  of  air  is 
excluded,  except  at  its  surface.  Under  these 
conditions  the  food  remains  moist,  but  neverthe- 
less does  not  undergo  its  ordinary  fermentations 
and  putrefactions,  and  may  be  preserved  for 
months  without  being  ruined.  The  food  in  such 
a  silo  may  be  taken  out  months  after  it  is  packed^ 
and  will  still  be  found  to  be  in  good  condition  foi 
food.  It  is  true  that  it  has  changed  its  charac- 
ter somewhat,  but  it  is  not  decayed,  and  is  eagerly 
eaten  by  cattle. 

We  are  yet  very  ignorant  of  the  nature  of  the 
changes  which  occur  in  the  food  while  in  the  silo. 
The  food  is  not  preserved  from  fermentation. 
When  the  silo  is  packed  slowly,  a  very  decided 
fermentation  occurs  by  which  the  mass  is  raised 
to  a  high  temperature  (140°  F.  to  160°  F.). 
This  heating  is  produced  by  certain  species  of 
bacteria  which  grow  readily  even  at  this  high 
temperature.  The  fermentation  uses  up  the  air 
in  the  silo  to  a  certain  extent  and  produces  a 
settling  of  the  material  which  still  further  ex- 
cludes air.  The  first  fermentation  soon  ceases, 
and  afterward  only  slow  changes  occur.  Certain 
acid-producing  bacteria  after  a  little  begin  to 
grow  slowly,  and  in  time  the  silage  is  rendered 
somewhat  sour  by  the  production  of  acetic  acid. 
But  the  exclusion  of  air,  the  close  packing,  and 
the  small  amount  of  moisture  appear  to  prevent 
the  growth  of  the  common  putrefactive  bacteria, 
and  the  silage  remains  good  for  a  long  time.  In 
other  methods  of  filling  the  silo,  the  food  is  very 
quickly  packed  and  densely  crowded  together  so 
as  to  exclude  as  much  air  as  possible  from  the 


114  THE  STORY  OF  GERM   LIFE. 

beginning.  Under  these  conditions  the  lack  of 
moisture  and  air  prevents  fermentative  action 
very  largely.  Only  certain  acid-producing  organ- 
isms grow,  and  these  very  slowly.  The  essential 
result  in  either  case  is  that  the  common  putrefac- 
tive bacteria  are  prevented  from  growing,  proba- 
bly by  lack  of  sufficient  oxygen  and  moisture, 
and  thus  the  decay  is  prevented.  The  closely 
packed  food  offers  just  the  same  unfavourable 
condition  for  the  growth  of  common  putrefactive 
bacteria  that  we  have  already  seen  offered  by  the 
hard-pressed  cheese,  and  the  bacteria  growth  is 
in  the  same  way  held  in  check.  Our  knowledge 
of  the  matter  is  as  yet  very  slight,  but  we  do 
know  enough  to  understand  that  the  successful 
management  of  a  silo  is  dependent  upon  the 
manipulation  of  bacteria. 

THE    FERTILITY    OF    THE    SOIL. 

The  farmer's  sole  duty  is  to  extract  food 
from  the  soil.  This  he  does  either  directly  by 
raising  crops,  or  indirectly  by  raising  animals 
which  feed  upon  the  products  of  the  soil.  In 
either  case  the  fertility  of  the  soil  is  the  funda- 
mental factor  in  his  success.  This  fertility  is  a 
gift  to  him  from  the  bacteria. 

Even  in  the  first  formation  of  soil  he  is  in  a 
measure  dependent  upon  bacteria.  Soil,  as  is  well 
known,  is  produced  in  large  part  by  the  crum- 
bling of  the  rocks  into  powder.  This  crumbling 
we  generally  call  weathering,  and  regard  it  as  due 
to  the  effect  of  moisture  and  cold  upon  the  rocks, 
together  with  the  oxidizing  action  of  the  air. 
Doubtless  this  is  true,  and  the  weathering  action 
is  largely  a  physical  and  chemical  one.  Never- 


BACTERIA  IN   NATURAL  PROCESSES.          115 

theless,  in  this  fundamental  process  of  rock  disin- 
tegration bacterial  action  plays  a  part,  though 
perhaps  a  small  one.  Some  species  of  bacteria, 
as  we  have  seen,  can  live  upon  very  simple  foods, 
finding  in  free  nitrogen  and  carbonates  sufficient- 
ly highly  complex  material  for  their  life.  These 
organisms  appear  to  grow  on  the  bare  surface  of 
rocks,  assimilating  nitrogen  from  the  air,  and  car- 
bon from  some  widely  diffused  carbonates  or  from 
the  COa  in  the  air.  Their  secreted  products  of 
an  acid  nature  help  to  soften  the  rocks,  and  thus 
aid  in  performing  the  first  step  in  weathering. 

The  soil  is  not,  however,  all  made  up  of  dis- 
integrated rocks.  It  contains,  besides,  various 
ingredients  which  combine  to  make  it  fertile. 
Among  these  are  various  sulphates  which  form 
important  parts  of  plant  foods.  These  sulphates 
appear  to  be  formed,  in  part,  at  least,  by  bacterial 
agency.  The  decomposition  of  proteids  gives 
rise,  among  other  things,  to  hydrogen  sulphide 
(H2S).  This  gas,  which  is  of  common  occurrence 
in  the  atmosphere,  is  oxidized  by  bacterial  growth 
into  sulphuric  acid,  and  this  is  the  basis  of  part 
of  the  soil  sulphates.  The  deposition  of  iron 
phosphates  and  iron  silicates  is  probably  also  in 
a  measure  aided  by  bacterial  action.  All  of  these 
processes  are  factors  in  the  formation  of  soil. 
Beyond  much  question  the  rock  disintegration 
which  occurs  everywhere  in  Nature  is  chiefly  the 
result  of  physical  and  chemical  changes,  but  there 
is  reason  for  believing  that  the  physical  and  chem- 
ical processes  are,  to  a  slight  extent  at  least,  as- 
sisted by  bacterial  life. 

A  more  important  factor  of  soil  fertility  is  its 
nitrogen  content,  without  which  it  is  complete- 
ly barren.  The  origin  of  these  nitrogen  ingre- 


Il6  THE   STORY   OF   GERM   LIFE. 

dients  has  been  more  or  less  of  a  puzzle.  Fertile 
soil  everywhere  contains  nitrates  and  other  nitro- 
gen compounds,  and  in  certain  parts  of  the  world 
there  are  large  accumulations  of  these  compounds, 
like  the  nitrate  beds  of  Chili.  That  they  have 
come  ultimately  from  the  free  atmospheric  nitro- 
gen seems  certain,  and  various  attempts  have  been 
made  to  explain  a  method  of  this  nitrogen  fixa- 
tion. It  has  been  suggested  that  electrical  dis- 
charges in  the  air  may  form  nitric  acid,  which 
would  readily  then  unite  with  soil  ingredients  to 
form  nitrates.  There  is  little  reason,  however, 
for  believing  this  to  be  a  very  important  factor. 
But  in  the  soil  bacteria  we  find  undoubtedly  an 
efficient  agency  in  this  nitrogen  fixation.  As  al- 
ready seen,  the  bacteria  are  able  to  seize  the  free 
atmospheric  nitrogen,  converting  it  into  nitrites 
and  nitrates.  We  have  also  learned  that  they 
can  act  in  connection  with  legumes  and  some 
other  plants,  enabling  them  to  fix  atmospheric  ni- 
trogen and  store  it  in  their  roots.  By  these  two 
means  the  nitrogen  ingredient  in  the  soil  is  pre- 
vented from  becoming  exhausted  by  the  processes 
of  dissipation  constantly  going  on.  Further,  by 
some  such  agency  must  we  imagine  the  original 
nitrogen  soil  ingredient  to  have  been  derived. 
Such  an  organic  agency  is  the  only  one  yet  dis- 
cerned which  appears  to  have  been  efficient  in 
furnishing  virgin  soil  with  its  nitrates,  and  we 
must  therefore  look  upon  bacteria  as  essential  to 
the  original  fertility  of  the  soil. 

But  in  another  direction  still  does  the  farmer 
depend  directly  upon  bacteria.  The  most  impor- 
tant factor  in  the  fertility  of  the  soil  is  the  part 
of  it  called  humus.  This  humus  is  very  complex, 
and  never  alike  in  different  soils.  It  contains  ni- 


BACTERIA   IN   NATURAL   PROCESSES.          117 

trogen  compounds  in  abundance,  together  with 
sulphates,  phosphates,  sugar,  and  many  other  sub- 
stances. It  is  this  which  makes  the  garden  soil 
different  from  sand,  or  the  rich  soil  different  from 
the  sterile  soil.  If  the  soil  is  cultivated  year  after 
year,  its  food  ingredients  are  slowly  but  surely 
exhausted.  Something  is  taken  from  the  humus 
each  year,  and  unless  this  be  replaced  the  soil 
ceases  to  be  able  to  support  life.  To  keep  up  a 
constant  yield  from  the  soil  the  farmer  under- 
stands that  he  must  apply  fertilizers  more  or  less 
constantly. 

This  application  of  fertilizers  is  simply  feed- 
ing the  crops.  Some  of  these  fertilizers  the  farm- 
er purchases,  and  knows  little  or  nothing  as  to 
their  origin.  The  most  common  method  of  feed- 
ing the  crops  is,  however,  by  the  use  of  ordinary 
barnyard  manure.  The  reason  why  this  material 
contains  plant  food  we  can  understand,  since  it 
is  made  of  the  undigested  part  of  food,  together 
with  all  the  urea  and  other  excretions  of  animals, 
and  contains,  therefore,  besides  various  minerals, 
all  of  the  nitrogenous  waste  of  animal  life.  These 
secretions  are  not  at  first  fit  for  plant  food.  The 
farmer  has  learned  by  experience  that  such  excre- 
tions, before  they  are  of  any  use  on  his  fields, 
must  undergo  a  process  of  slow  change,  which 
is  sometimes  called  ripening.  Fresh  manure  is 
sometimes  used  on  the  fields,  but  it  is  only  made 
use  of  by  the  plants  after  the  ripening  process 
has  occurred.  Fresh  animal  excretions  are  of 
little  or  no  value  as  a  fertilizer.  The  farmer, 
therefore,  commonly  allows  it  to  remain  in  heaps 
for  some  time,  and  it  undergoes  a  slow  change, 
which  gradually  converts  it  into  a  condition  in 
which  it  can  be  used  by  plants.  This  ripening  is 


Il8  THE   STORY  OF  GERM   LIFE. 

readily  explained  by  the  facts  already  considered. 
The  fresh  animal  secretions  consist  of  various 
highly  complex  compounds  of  nitrogen,  and  the 
ripening  is  a  process  of  their  decomposition.  The 
proteids  are  broken  to  pieces,  and  their  nitrogen 
elements  reduced  to  the  form  of  nitrates,  leucin, 
etc.,  or  even  to  ammonia  or  free  nitrogen.  Fur- 
ther, a  second  process  occurs,  the  process  of 
oxidation  of  these  nitrogen  compounds  already 
noticed,  and  the  ammonia  and  nitrites  resulting 
from  the  decomposition  are  built  into  nitrates. 
In  short,  in  this  ripening  manure  the  processes 
noticed  in  the  first  part  of  this  chapter  are  taking 
place,  by  which  the  complex  nitrogenous  bodies 
are  first  reduced  and  then  oxidized  to  form  plant 
food.  The  ripening  of  manure  is  both  an  ana- 
lytical and  a  synthetical  process.  By  the  analy- 
sis, proteids  and  other  bodies  are  broken  into  very 
simple  compounds,  some  of  them,  indeed,  being 
dissipated  into  the  air,  but  other  portions  are  re- 
tained and  then  oxidized,  and  these  latter  become 
the  real  fertilizing  materials.  Through  the  agency 
of  bacteria  the  compost  heap  thus  becomes  the 
great  source  of  plant  food  to  the  farmer.  Into 
this  compost  heap  he  throws  garbage,  straw,  vege- 
table and  animal  substances  in  general,  or  any 
organic  refuse  which  may  be  at  hand.  The  vari- 
ous bacteria  seize  it  all,  and  cause  the  decomposi- 
tion which  converts  it  into  plant  food  again.  The 
rotting  of  the  compost  heap  is  thus  a  gigantic 
cultivation  of  bacteria. 

This  knowledge  of  the  ripening  process  is  fur- 
ther teaching  the  farmer  how  to  prevent  waste. 
In  the  ordinary  decomposition  of  the  compost 
heap  not  an  inconsiderable  portion  of  the  nitro- 
gen is  lost  in  the  air  by  dissipation  as  ammonia 


BACTERIA   IN   NATURAL   PROCESSES.          119 

or  free  nitrogen.  Even  his  nitrates  may  be  thus 
lost  by  bacterial  action.  This  portion  is  lost  to 
the  farmer  completely,  and  he  can  only  hope  to 
replace  it  either  by  purchasing  nitrates  in  the 
form  of  commercial  fertilizers,  or  by  reclaiming  it 
from  the  air  by  the  use  of  the  bacterial  agencies 
already  noticed.  With  the  knowledge  now  at  his 
command  he  is  learning  to  prevent  this  waste. 
In  the  decomposition  one  large  factor  of  loss  is 
the  ammonia,  which,  being  a  gas,  is  readily  dis- 
sipated into  the  air.  Knowing  this  common  re- 
sult of  bacterial  action,  the  scientist  has  told  the 
farmer  that,  by  adding  certain  common  chemic- 
als to  his  decomposing  manure  heap,  chemicals 
which  will  readily  unite  with  ammonia,  he  may 
retain  most  of  the  nitrogen  in  this  heap  in  the 
form  of  ammonia  salts,  which,  once  formed,  no 
longer  show  a  tendency  to  dissipate  into  the  air. 
Ordinary  gypsum,  or  superphosphates,  or  plaster 
will  readily  unite  with  ammonia,  and  these  added 
to  the  manure  heap  largely  counteract  the  tend- 
ency of  the  nitrogen  to  waste,  thus  enabling  the 
farmer  to  put  back  into  his  soil  most  of  the  nitro- 
gen which  was  extracted  from  it  by  his  crops 
and  then  used  by  his  stock.  His  vegetable  crcyps 
raise  the  nitrates  into  proteids.  His  animals  feed 
upon  the  proteids,  and  perform  his  work  or  fur- 
nish him  with  milk.  Then  his  bacteria  stock 
take  the  excreted  or  refuse  nitrogen,  and  in  his 
manure  heap  turn  it  back  again  into  nitrates 
ready  to  begin  the  circle  once  more.  This  might 
go  on  almost  indefinitely  were  it  not  for  two 
facts  :  the  farmer  sends  nitrogenous  material  off 
his  farm  in  the  milk  or  grains  or  other  nitro- 
genous products  which  he  sells,  and  the  de- 
composition processes,  as  we  have  seen,  dissi- 


120  THE   STORY  OF   GERM   LIFE. 

pate  some  of  the  nitrogen  into  the  air  as  free  ni- 
trogen. 

To  meet  this  emergency  and  loss  the  farmer 
has  another  method  of  enriching  the  soil,  again 
depending  upon  bacteria.  This  is  the  so-called 
green  manuring.  Here  certain  plants  which  seize 
nitrogen  from  the  air  are  cultivated  upon  the  field 
to  be  fertilized,  and,  instead  of  harvesting  a 
crop,  it  is  ploughed  into  the  soil.  Or  perhaps 
the  tops  may  be  harvested,  the  rest  being 
ploughed  into  the  soil.  The  vegetable  material 
thus  ploughed  in  lies  over  a  season  and  enriches 
the  soil.  Here  the  bacteria  of  the  soil  come  into 
play  in  several  directions.  First,  if  the  crop 
sowed  be  a  legume,  the  soil  bacteria  assist  it  to 
seize  the  nitrogen  from  the  air.  The  only  plants 
which  are  of  use  in  this  green  manuring  are  those 
which  can,  through  the  agency  of  bacteria,  obtain 
nitrogen  from  the  air  and  store  it  in  their  roots. 
Second,  after  the  crop  is  ploughed  into  the  soil 
various  decomposing  bacteria  seize  upon  it,  pulling 
the  compounds  to  pieces.  The  carbon  is  largely 
dissipated  into  the  air  as  carbonic  dioxide,  where 
the  next  generation  of  plants  can  get  hold  of  it. 
The  minerals  and  the  nitrogen  remain  in  the  soil. 
The  nitrogenous  portions  go  through  the  same 
series  of  decomposition  and  synthetical  changes 
already  described,  and  thus  eventually  the  nitro- 
gen seized  from  the  air  by  the  combined  action 
of  the  legumes  and  the  bacteria  is  converted  into 
nitrates,  and  will  serve  for  food  for  the  next  set 
of  plants  grown  on  the  same  soil.  Here  is  thus  a 
practical  method  of  using  the  nitrogen  assimila- 
tion powers  of  bacteria,  and  reclaiming  nitrogen 
from  the  air  to  replace  that  which  has  been  lost. 

Thus  it  is  that  the  farmer's  nitrogen  problem 


BACTERIA   IN   NATURAL   PROCESSES.          12 1 

of  the  fertile  soil  appears  to  resolve  itself  into  a 
proper  handling  of  bacteria.  These  organisms 
have  stocked  his  soil  in  the  first  place.  They 
convert  all  of  his  compost  heap  wastes  into  simple 
bodies,  some  of  which  are  changed  into  plant 
foods,  while  others  are  at  the  same  time  lost. 
Lastly,  they  may  be  made  to  reclaim  this  lost 
nitrogen,  and  the  farmer,  so  soon  as  he  has 
requisite  knowledge  of  these  facts,  will  be  able 
to  keep  within  his  control  the  supply  of  this  im- 
portant element.  The  continued  fertility  of  the 
soil  is  thus  a  gift  from  the  bacteria. 

BACTERIA    AS    SOURCES    OF    TROUBLE    TO    THE 
FARMER. 

While  the  topics  already  considered  comprise 
the  most  important  factors  in  agricultural  bacte- 
riology, the  farmer's  relations  to  bacteria  do 
not  end  here.  These  organisms  come  incidentally 
into  his  life  in  many  ways.  They  are.  not  always 
his  aids  as  they  are  in  most  of  the  instances  thus 
far  cited.  They  produce  disease  in  his  cattle,  as 
will  be  noticed  in  the  next  chapter.  Bacteria  are 
agents  of  decomposition,  and  they  are  just  as 
likely  to  decompose  material  which  the  farmer 
wishes  to  preserve  as  they  are  to  decompose  ma- 
terial which  the  farmer  desires  to  undergo  the 
process  of  decay.  They  are  as  ready  to  attack 
his  fruits  and  vegetables  as  to  ripen  his  cream. 
The  skin  of  fruits  and  vegetables  is  a  moderately 
good  protection  of  the  interior  from  the  attack 
of  bacteria;  but  if  the  skin  be  broken  in  any 
place,  bacteria  get  in  and  cause  decay,  and  to 
prevent  it  the  farmer  uses  a  cold  cellar.  The 
bacteria  prevent  the  farmer  from  preserving 


122  THE  STORY  OF  GERM   LIFE. 

meats  for  any  length  of  time  unless  he  checks 
their  growth  in  some  way.  They  get  into  the 
eggs  of  his  fowls  and  ruin  them.  Their  trouble- 
some nature  in  the  dairy  in  preventing  the  keep- 
ing of  milk  has  already  been  noticed.  If  he 
plants  his  seeds  in  very  moist,  damp  weather, 
the  soil  bacteria  cause  too  rapid  a  decomposition 
of  the  seeds  and  they  rot  in  the  ground  instead 
of  sprouting.  They  produce  disagreeable  odours, 
and  are  the  cause  of  most  of  the  peculiar  smells, 
good  and  bad,  around  the  barn.  They  attack 
the  organic  matter  which  gets  into  his  well  or 
brook  or  pond,  decomposing  it,  filling  the  water 
with  disagreeable  and  perhaps  poisonous  products 
which  render  it  unfit  to  drink.  They  not  only  aid 
in  the  decay  of  the  fallen  tree  in  his  forests,  but 
in  the  same  way  attack  the  timber  which  he 
wishes  to  preserve,  especially  if  it  is  kept  in  a 
moist  condition.  Thus  they  contribute  largely 
to  the  gradual  destruction  of  wooden  structures. 
It  is  therefore  the  presence  of  these  organisms 
which  forces  him  to  dry  his  hay,  to  smoke  his 
hams,  to  corn  his  beef,  to  keep  his  fruits  and 
vegetables  cool  and  prevent  skin  bruises,  to  ice 
his  dairy,  to  protect  his  timber  from  rain,  to  use 
stone  instead  of  wooden  foundations  for  build- 
ings, etc.  In  general,  when  the  farmer  desires 
to  get  rid  of  any  organic  refuse,  he  depends  upon 
bacteria,  for  they  are  his  sole  agents  (aside  from 
fire)  for  the  final  destruction  of  organic  matter. 
When  he  wishes  to  convert  waste  organic  refuse 
into  fertilizing  material,  he  uses  the  bacteria  of 
his  compost  heap.  On  the  other  hand,  whenever 
he  desires  to  preserve  organic  material,  the 
bacteria  are  the  enemies  against  which  he  must 
carefully  guard. 


BACTERIA   IN   NATURAL   PROCESSES.          123 

Thus  the  farmer's  life  from  year's  end  to  year's 
end  is  in  most  intimate  association  with  bacteria. 
Upon  them  he  depends  to  insure  the  continued 
fertility  of  his  soil  and  the  constant  continued 
production  of  good  crops.  Upon  them  he  de- 
pends to  turn  into  plant  food  all  the  organic  ref- 
use from  his  house  or  from  his  barn.  Upon 
them  he  depends  to  replenish  his  stock  of  nitrogen. 
It  is  these  organisms  which  furnish  his  dairy  with 
its  butter  flavours  and  with  the  taste  of  its  cheese. 
But,  on  the  other  hand,  against  them  he  must  be 
constantly  alert.  All  his  food  products  must  be 
protected  from  their  ravages.  A  successful  farm- 
er's life,  then,  largely  resolves  itself  into  a  skilful 
management  of  bacterial  activity.  To  aid  them 
in  destroying  or  decomposing  everything  which  he 
does  not  desire  to  preserve,  and  to  prevent  their 
destroying  the  organic  material  which  he  wishes  to 
keep  for  future  use,  is  the  object  of  a  considerable 
portion  of  farm  labour ;  and  the  most  successful 
farmer  to-day,  and  we  believe  the  most  successful 
farmer  of  the  future,  is  the  one  who  most  intelli- 
gently and  skilfully  manipulates  these  gigantic 
forces  furnished  him  by  the  growth  of  his  micro- 
scopical allies. 

RELATION  OF  BACTERIA  TO  COAL. 

Another  one  of  Nature's  processes  in  which 
bacteria  have  played  an  important  part  is  in  the 
formation  of  coal.  It  is  unnecessary  to  emphasize 
the  importance  of  coal  in  modern  civilization. 
Aside  from  its  use  as  fuel,  upon  which  civilization 
is  dependent,  coal  is  a  source  of  an  endless  variety 
of  valuable  products.  It  is  the  source  of  our 
illuminating  gas,  and  ammonia  is  one  of  the  prod- 


124  THE  STORY  OF  GERM  LIFE. 

ucts  of  the  gas  manufacture.  From  the  coal 
also  comes  coal  tar,  the  material  from  which  such 
a  long  series  of  valuable  materials,  as  aniline 
colours,  carbolic  acid,  etc.,  is  derived.  The  list  of 
products  which  we  owe  to  coal  is  very  long,  and 
the  value  of  this  material  is  hardly  to  be  over- 
rated. In  the  preparation  of  these  ingredients 
from  coal  bacteria  do  not  play  any  part.  Most 
of  them  are  derived  by  means  of  distillation.  But 
when  asked  for  the  agents  which  have  given  us 
the  coal  of  the  coal  beds,  we  shall  find  that  here, 
too,  we  owe  a  great  debt  to  bacteria. 

Coal,  as  is  well  known,  has  come  from  the  ac- 
cumulation of  the  luxuriant  vegetable  growth  of 
the  past  geological  ages.  It  has  therefore  been 
directly  furnished  us  by  the  vegetation  of  the 
green  plants  of  the  past,  and,  in  general,  it  repre- 
sents so  much  carbonic  dioxide  which  these 
plants  have  extracted  from  the  atmosphere.  But 
while  the  green  plants  have  been  the  active 
agents  in  producing  this  assimilation,  bacteria 
have  played  an  important  part  in  coal  manufac- 
ture in  two  different  directions.  The  first  ap- 
pears to  be  in  furnishing  these  plants  with 
nitrogen.  Without  a  store  of  fixed  nitrogen  in 
the  soil  these  carboniferous  plants  could  not  have 
grown.  This  matter  has  already  been  considered. 
We  have  no  very  absolute  knowledge  as  to  the 
agency  of  bacteria  in  furnishing  nitrogen  for  this 
vegetation  in  past  ages,  but  there  is  every  reason 
to  believe  that  in  the  past,  as  in  the  present,  the 
chief  source  of  organic  nitrogen  has  been  from 
the  atmosphere  and  derived  from  the  atmos- 
phere through  the  agency  of  bacteria.  In  the 
absence  of  any  other  known  factor  we  may  be 
pretty  safe  in  the  assumption  that  bacteria  played 


BACTERIA  IN   NATURAL   PROCESSES.          125 

an  important  part  in  this  nitrogen  fixation,  and 
that  bacteria  must  therefore  be  regarded  as  the 
agents  which  have  furnished  us  the  nitrogen 
stored  in  the  coal. 

But  in  a  later  stage  of  coal  formation  bacteria 
have  contributed  more  directly  to  the  formation  of 
coal.  Coal  is  not  simply  accumulated  vegetation. 
The  coal  of  our  coal  beds  is  very  different  in  its 
chemical  composition  from  the  wood  of  the  trees. 
It  contains  a  much  higher  percentage  of  carbon 
and  a  lower  percentage  of  hydrogen  and  oxygen 
than  ordinary  vegetable  substances.  The  conver- 
sion of  the  vegetation  of  the  carboniferous  ages 
into  coal  was  accompanied  by  a  gradual  loss  of 
hydrogen  and  a  consequent  increase  in  the  per- 
centage of  carbon.  It  is  this  change  that  has 
added  to  the  density  of  the  substance  and  makes 
the  greater  value  of  coal  as  fuel.  There  is  little 
doubt  now  as  to  the  method  by  which  this  woody 
material  of  the  past  has  been  converted  into  coal. 
The  same  process  appears  to  be  going  on  in  a 
similar  manner  to-day  in  the  peat  beds  of  various 
northern  countries.  The  fallen  vegetation,  trees, 
trunks,  branches,  and  leaves,  accumulate  in 
masses,  and,  when  the  conditions  of  moisture  and 
temperature  are  right,  begin  to  undergo  a  fer- 
mentation. Ordinarily  this  action  of  bacteria, 
as  already  noticed,  produces  an  almost  complete 
though  slow  oxidation  of  the  carbon,  and  results 
in  the  total  decay  of  the  vegetable  matter.  But 
if  the  vegetable  mass  be  covered  by  water  and 
mud  under  proper  conditions  of.  moisture  and  tem- 
perature, a  different  kind  of  fermentation  arises 
which  does  not  produce  such  complete  decay. 
The  covering  of  water  prevents  the  access  of 
oxygen  to  the  fermenting  mass,  an  oxidation  of 


126  THE  STORY  OF  GERM   LIFE.. 

the  carbon  is  largely  prevented,  and  the  vegetable 
matter  slowly  changes  its  character.  Under  the 
influence  of  this  slow  fermentation,  aided,  proba- 
bly by  pressure,  the  mass  becomes  more  and  more 
solid  and  condensed,  its  woody  character  becomes 
less  and  less  distinct,  and  there  is  a  gradual  loss 
of  the  hydrogen  and  the  oxygen.  Doubtless 
there  is  a  loss  of  carbon  also,  for  thqre  is  an  evo- 
lution of  marsh  gas  which  contains  carbon.  But 
in  this  slow  fermentation  .taking  place  under  the 
water  in  peat  bogs  and  marshes  the  carbon  loss 
is  relatively  small ;  the  woody  material  does  not 
become  completely  oxidized,  as  it  does  in  free 
operations  of  decay.  The  loss  of  hydrogen  and 
oxygen  from  the  mass  is  greater  than  that  of 
carbon,  and  the  percentage  of  carbon  therefore  in- 
creases. This  is  not  the  ordinary  kind  of  fermen- 
tation that  goes  on  in  vegetable  accumulations. 
It  requires  special  conditions  and  possibly  special 
kinds  of  fermenting  organisms.  Peat  is  not 
formed  in  all  climates.  In  warm  regions,  or 
where  the  woody  matter  is  freely  exposed  to  the 
air,  the  fermentation  of  vegetable  matter  is  more 
complete,  and  it  is  entirely  destroyed  by  oxida- 
tion. It  is  only  in  colder  regions  and  when  cov- 
ered with  water  that  the  destruction  of  the  organic 
matter  stops  short  of  decay.  But  such  incom- 
plete fermentation  is  still  going  on  in  many  parts 
of  the  world,  and  by  its  means  vegetable  ac- 
c'umulations  are  being  converted  into  peat. 

This  formation  of  peat  appears  to  be  a  first 
step  in  the  formation  of  denser  coal.  By  a  con- 
tinuation of  the  same  processes  the  mass  becomes 
still  more  dense  and  solid.  As  we  pass  from  the 
top  to  the  bottom  of  such  an  accumulation  of 
peat,  we  find  it  becoming  denser  and  denser,  and 


BACTERIA  IN  NATURAL   PROCESSES.          127 

at  the  bottom  it  is  commonly  of  a  hard  consist- 
ence, brownish  in  colour,  and  with  only  slight 
traces  of  the  original  woody  structure.  Such 
material  is  called  lignite.  It  contains  a  higher 
percentage  of  carbon  than  peat,  but  a  lower  per- 
centage than  coal,  and  is  plainly  a  step  in  coal  for- 
mation. But  the  process  goes  on,  the  hydrogen 
and  oxygen  loss  continuing  until  there  is  finally 
produced  true  coal. 

If  this  is  the  correct  understanding  of  the  for- 
mation of  coal,  we  see  that  we  have  plainly  a  pro- 
cess in  which  bacterial  life  has  had  a  large  and 
important  share.  We  are,  of  course,  densely 
ignorant  of  the  exact  processes  going  on.  We 
know  nothing  positively  as  to  the  kind  of  micro- 
organisms which  produce  this  slow,  peculiar  fer- 
mentation. As  yet,  the  fermentation  going  on  in 
the  formation  of  the  peat  has  not  been  studied 
by  the  bacteriologists,  and  we  do  not  know  from 
direct  experiment  that  it  is  a  matter  of  bacterial 
action.  It  has  been  commonly  regarded  as  sim- 
ply a  slow  chemical  change,  but  its  general  simi- 
larity to  other  fermentative  processes  is  so  great 
that  we  can  have  little  hesitation  in  attributing  it 
to  micro-organisms,  and  doubtless  to  some  forms 
of  plants  allied  to  bacteria.  There  is  no  reason 
for  doubting  that  bacteria  existed  in  the  geologi- 
cal ages  with  essentially  the  same  powers  as 
they  now  possess,  and  to  some  forms  of  bacteria 
which  grow  in  the  absence  of  oxygen  can  we 
probably  attribute  the  slow  change  which  has 
produced  coal.  Here,  then,  is  another  great 
source  of  wealth  in  Nature  for  which  we  are  de- 
pendent upon  bacteria.  While,  of  course,  water 
and  pressure  were  very  essential  factors  in  the 
deposition  of  coal,  it  was  a  peculiar  kind  of  fer- 
9 


128  THE  STORY  OF  GERM   LIFE. 

mentation  occurring  in  the  vegetation  that 
brought  about  the  chemical  changes  in  it  which 
resulted  in  its  transformation  into  coal.  The  vege- 
tation of  the  carboniferous  age  was  dependent 
upon  the  nitrogen  fixed  by  the  bacteria,  and  to 
these  organisms  also  do  we  owe  the  fact  that  this 
vegetation  was  stored  for  us  in  the  rocks. 


CHAPTER   V. 

PARASITIC    BACTERIA    AND    THEIR    RELATION    TO 
DISEASE. 

PERHAPS  the  most  universally  known  fact  in 
regard  to  bacteria  is  that  they  are  the  cause  of 
disease.  It  is  this  fact  that  has  made  them  ob- 
jects of  such  wide  interest.  This  is  the  side  of 
the  subject  that  first  attracted  attention,  has  been 
most  studied,  and  in  regard  to  which  there  has 
been  the  greatest  accumulation  of  evidence.  So 
persistently  has  the  relation  of  bacteria  to  disease 
been  discussed  and  emphasized  that  the  majority 
of  readers  are  hardly  able  to  disassociate  the  two. 
To  most  people  the  very  word  bacteria  is  almost 
equivalent  to  disease,  and  the  thought  of  swallow- 
ing microbes  in  drinking  water  or  milk  is  decid- 
edly repugnant  and  alarming.  In  the  public  mind 
it  is  only  necessary  to  demonstrate  that  an  article 
holds  bacteria  to  throw  it  under  condemnation. 

We  have  already  seen  that  bacteria  are  to  be 
regarded  as  agents  for  good,  and  that  from  their 
fundamental  relation  to  plant  life  they  must  be 
looked  upon  as  our  friends  rather  than  as  our 
enemies.  It  is  true  that  there  is  another  side  to 


PARASITIC  BACTERIA.  129 

the  story  which  relates  to  the  parasitic  species. 
These  parasitic  forms  may  do  us  direct  or  indi- 
rect injury.  But  the  species  of  bacteria  which  are 
capable  of  doing  us  any  injury,  the  pathogenic  bac- 
teria, are  really  very  few  compared  to  the  great 
host  of  species  which  are  harmless.  A  small 
number  of  species,  perhaps  a  score  or  two,  are 
pathogenic,  while  a  much  larger  number,  amount- 
ing to  hundreds  and  perhaps  thousands  of  species, 
are  perfectly  harmless.  This  latter  class  do  no  in- 
jury even  though  swallowed  by  man  in  thousands. 
They  are  not  parasitic,  and  are  unable  to  grow  in 
the  body  of  man.  Their  presence  is  entirely  con- 
sistent with  the  most  perfect  health,  and,  indeed, 
there  are  some  reasons  for  believing  that  they 
are  sometimes  directly  beneficial  to  health.  It  is 
entirely  unjust  to  condemn  all  bacteria  because  a 
few  chance  to  produce  mischief.  Bacteria  in  gen- 
eral are  agents  for  good  rather  than  ill. 

There  are,  however,  some  species  which  cause 
mankind  much  trouble  by  interfering  in  one  way 
or  another  with  the  normal  processes  of  life. 
These  pathogenic  bacteria,  or  disease  germs,  do 
not  all  act  alike,  but  bring  about  injury  to  man  in 
a  number  of  different  ways.  We  may  recognise 
two  different  classes  among  them,  which,  how- 
ever, we  shall  see  are  connected  by  intermediate 
types.  These  two  classes  are,  first,  the  patho- 
genic bacteria,  which  are  not  strictly  parasitic  but 
live  free  in  Nature;  and,  second,  those  which  live 
as  true  parasites  in  the  bodies  of  man  or  other  ani- 
mals. To  understand  the  real  relation  of  these 
two  classes,  we  must  first  notice  the  method  by 
which  bacteria  in  general  produce  disease. 


130  THE   STORY  OF   GERM   LIFE. 

METHOD    BY    WHICH    BACTERIA    PRODUCE 
DISEASE. 

Since  it  was  first  clearly  recognised  that  cer- 
tain species  of  bacteria  have  the  power  of  pro- 
ducing disease,  the  question  as  to  how  they  do 
so  has  ever  been  a  prominent  one.  Even  if  they 
do  grow  in  the  body,  why  should  their  presence 
give  rise  to  the  symptoms  characterizing  dis- 
ease ?  Various  answers  to  this  question  have 
been  given  in  the  past.  It  has  been  suggested 
that  in  their  growth  they  consume  the  food  of 
the  body  and  thus  exhaust  it ;  that  they  produce 
an  oxidation  of  the  body  tissues,  or  that  they 
produce  a  reduction  of  these  tissues,  or  that 
they  mechanically  interfere  with  the  circulation. 
None  of  these  suggestions  have  proved  of  much 
value.  Another  view  was  early  advanced,  and  has 
stood  the  test  of  time.  This  claim  is  that  the 
bacteria  while  growing  in  the  body  produce  poi- 
sons, and  these  poisons  then  have  a  direct  action 
on  the  body.  We  have  already  noticed  that  bac- 
teria during  their  growth  in  any  medium  produce 
a  large  number  of  biproducts  of  decomposition. 
We  noticed  also  that  among,  these  biproducts 
there  are  some  which  have  a  poisonous  nature  ; 
so  poisonous  are  they  that  when  inoculated  into 
the  body  of  an  animal  they  may  -produce  poison 
ing  and  death.  We  have  only  to  suppose  that  the 
pathogenic  bacteria,  when  growing  as  parasites  in 
man,  produce  such  poisons,  and  we  have  at  once 
an  explanation  of  the  method  by  which  they  give 
rise  to  disease. 

This  explanation  of  germ  disease  is  more  than 
simple  theory.  It  has  been  in  many  cases  clearly 
demonstrated.  It  has  been  found  that  the  bac- 


PARASITIC   BACTERIA.  131 

teria  which  cause  diphtheria,  tetanus,  typhoid, 
tuberculosis,  and  many  other  diseases,  produce, 
even  when  growing  in  common  culture  media, 
poisons  which  are  of  a  very  violent  nature.  These 
poisons  when  inoculated  into  the  bodies  of  ani- 
mals give  rise  to  much  the  same  symptoms  as 
the  bacteria  do  themselves  when  growing  as  para- 
sites in  the  animals.  The  chief  difference  in  the 
results  from  inoculating  an  animal  with  the  poison 
and  with  the  living  bacteria  is  in  the  rapidity  of 
the  action.  When  the  poison  is  injected  the  poi- 
soning symptoms  are  almost  immediately  seen ;  but 
when  the  living  bacteria  are  inoculated  the  effect 
is  only  seen  after  several  days  or  longer,  not,  in 
short,  until  the  inoculated  bacteria  have  had  time 
enough  to  grow  in  the  body  and  produce  the  poi- 
son in  quantity.  It  has  not  by  any  means  been 
shown  that  all  pathogenic  germs  produce  their 
effect  in  this  way,  but  it  has  been  proved  to  be 
the  real  method  in  quite  a  number  of  cases,  and 
is  extremely  probable  in  others.  While  some 
bacteria  perhaps  produce  results  by  a  different 
method,  we  must  recognise  the  production  of  poi- 
sons as  at  all  events  the  common  direct  cause  of 
the  symptoms  of  disease.  This  explanation  will 
enable  us  more  clearly  to  understand  the  relation 
of  different  bacteria  to  disease. 


PATHOGENIC    GERMS    WHICH    ARE    NOT    STRICTLY 
PARASITIC. 

Recognising  that  bacteria  may  produce  poi- 
sons, we  readily  see  that  it  is  not  always  neces- 
sary that  they  should  be  parasites  in  order  to 
produce  trouble.  In  their  ordinary  growth  in 
Nature  such  bacteria  will  produce  no  trouble. 


132  THE  STORY  OF   GERM   LIFE. 

The  poisons  will  be  produced  in  decaying  mate- 
rial but  will  seldom  be  taken  into  the  human 
body.  These  poisons,  produced  in  the  first 
stages  of  putrefaction,  are  oxidized  by  further 
stages  of  decomposition  into  harmless  products. 
But  should  it  happen  that  some  of  these  bacteria 
obtained  a  chance  to  grow  vigorously  for  a  while 
in  organic  products  that  are  subsequently  swal- 
lowed as  man's  food,  it  is  plain  that  evil  results 
might  follow.  If  such  food  is  swallowed  by  man 
after  the  bacteria  have  produced  their  poisonous 
bodies,  it  will  tend  to  produce  an  immediate  poi- 
soning of  his  system.  The  effect  may  be  sudden 
and  severe  if  considerable  quantity  of  the  poison- 
ous material  is  swallowed,  or  slight  but  protracted 
if  small  quantities  are  repeatedly  consumed  in 
food.  Such  instances  are  not  uncommon.  Well- 
known  examples  are  cases  of  ice-cream  poison- 
ing, poisoning  from  eating  cheese  or  from  drink- 
ing milk,  or  in  not  a  few  instances  from  eating 
fish  or  meats  within  which  bacteria  have  had 
opportunity  for  growth.  In  all  these  cases  the 
poison  is  swallowed  in  quantity  sufficient  to  give 
rise  quickly  to  severe  symptoms,  sometimes  re- 
sulting fatally,  and  at  other  times  passing  off  as 
soon  as  the  body  succeeds  in  throwing  off  the 
poisons.  In  other  cases  still,  however,  the 
amount  of  poison  swallowed  may  be  very  slight, 
too  slight  to  produce  much  effect  unless  the  same 
be  consumed  repeatedly.  All  such  trouble  may 
be  attributed  to  fermented  or  partly  decayed 
food.  It  is  difficult  to  distinguish  such  instances 
from  others  produced  in  a  slightly  different  way, 
as  follows : 

It  may  happen  that  the  bacteria  which  grow 
in  food  products  continue  to   grow  in  the  food 


PARASITIC   BACTERIA.  133 

even  after  it  is  swallowed  and  has  passed  into 
the  stomach  or  intestines.  This  appears  particu- 
larly true  of  milk  bacteria.  Under  these  condi- 
tions the  bacteria  are  not  in  any  proper  sense 
parasitic,  since  they  are  simply  living  in  and 
feeding  upon  the  same  food  which  they  consume 
outside  the  body,  and  are  not  feeding  upon  the 
tissues  of  man.  The  poisons  which  they  produce 
will  continue  to  be  developed  as  long  as  the  bac- 
teria continue  to  grow,  whether  in  a  milk  pail  or 
a  human  stomach.  If  now  the  poisons  are  ab- 
sorbed by  the  body,  they  may  produce  a  mild  or 
severe  disease  which  will  be  more  or  less  lasting, 
continuing  perhaps  as  long  as  the  same  food  and 
the  same  bacteria  are  supplied  to  the  individual. 
The  most  important  disease  of  this  class  appears 
to  be  the  dreaded  cholera  infantum,  so  common 
among  infants  who  feed  upon  cow's  milk  in  warm 
weather.  It  is  easy  to  understand  the  nature  of 
this  disease  when  we  remember  the  great  number 
of  bacteria  in  milk,  especially  in  hot  weather, 
and  when  we  remember  that  the  delicate  organ- 
ism of  the  infant  will  be  thrown  at  once  into 
disorder  by  slight  amounts  of  poison  which  would 
have  no  appreciable  effect  upon  the  stronger 
adult.  We  can  easily  understand,  further,  how 
the  disease  readily  yields  to  treatment  if  care 
is  taken  to  sterilize  the  milk  given  to  the  pa- 
tient. 

We  do  not  know  to-day  .the  extent  of  the 
troubles  which  are  produced  by  bacteria  of  this 
sort.  They  will,  of  course,  be  chiefly  connected 
with  our  food  products,  and  commonly,  though 
not  always,  will  affect  the  digestive  functions.  It 
is  probable  that  many  of  the  cases  of  summer 
diarrhoea  are  produced  by  some  such  cause,  and 


134  THE  STORY  OF  GERM   LIFE. 

if  they  could  be  traced  to  their  source  would  be 
found  to  be  produced  by  bacterial  poisons  swal- 
lowed with  food  or  drink,  or  by  similar  poisons 
produced  by  bacteria  growing  in  such  food  after 
it  is  swallowed  by  the  individual.  In  hot  weather, 
when  bacteria  are  so  abundant  everywhere  and 
growing  so  rapidly,  it  is  impossible  to  avoid  such 
dangers  completely  without  exercising  over  all 
food  a  guard  which  would  be  decidedly  oppress- 
ive. It  is  well  to  bear  in  mind,  however,  that 
the  most  common  and  most  dangerous  source  of 
such  poisons  is  milk  or  its  products,  and  for  this 
reason  one  should  hesitate  to  drink  milk  in  hot 
weather  unless  it  is  either  quite  fresh  or  has  been 
boiled  to  destroy  its  bacteria. 

PATHOGENIC    BACTERIA    WHICH    ARE    TRUE 
PARASITES. 

This  class  of  pathogenic  bacteria  includes 
those  which  actually  invade  the  body  and  feed 
upon  its  tissues  instead  of  living  simply  upon 
swallowed  food.  It  is  difficult,  however,  to  draw 

any  sharp  line  sep- 
arating the  two 
classes.  The  bac- 
teria which  cause 
diphtheria  (Fig. 
28),  for  instance, 
do  not  really  in- 
FIG.  ^.-Diphtheria  bacillus.  va^e  the  body. 

They  grow  in  the 

throat,  attached  to  its  walls,  and  are  confined  to 
this  external  location  or  to  the  superficial  tissues. 
This  bacillus  is,  in  short,  only  found  in  the  mouth 
and  throat,  and  is  practically  confined  to  the  so- 


PARASITIC  BACTERIA.  135 

called  false  membranes.  It  never  enters  any  of 
the  tissues  of  the  body,  although  attached  to  the 
mucous  membrane.  It  grows  vigorously  in  this 
membrane,  and  there  secretes  or  in  some  way 
produces  extremely  violent 
poisons.  These  poisons 
are  then  absorbed  by  the 
body  and  give  rise  to  the 
general  symptoms  of  the 
disease.  Much  the  same  is 
true  of  the  bacillus  which 
causes  tetanus  or  lockjaw  Y\G.  ^g.— Tetanus  bacillus. 
(Fig.  29).  This  bacillus  is 

commonly  inoculated  into  the  flesh  of  the  victim 
by  a  wound  made  with  some  object  which  has 
been  lying  upon  the  earth  where  the  bacillus 
lives.  The  bacillus  grows  readily  after  being  in- 
oculated, but  it  is  localized  at  the  point  of  the 
wound,  without  invading  the  tissue  to  any  extent. 
It  produces,  however,  during  its  growth  several 
poisons  which  have  been  separated  and  studied. 
Among  them  are  some  of  the  most  violent  poi- 
sons of  which  we  have  any  knowledge.  While 
the  bacillus  grows  in  the  tissues  around  the 
wound  it  secretes  these  poisons,  which  are  then 
absorbed  by  the  body  generally.  Their  poison- 
ing effects  produce  the  violent  symptoms  of  the 
disease.  Of  much  the  same  nature  is  Asiatic 
cholera.  This  is  caused  by  a  bacillus  which  is 
able  to  grow  rapidly  in  the  intestines,  feeding 
perhaps  in  part  on  the  food  in  the  intestines  and 
perhaps  in  part  upon  the  body  secretions.  To 
a  slight  extent  also  it  appears  to  be  able  to  in- 
vade the  tissues  of  the  body,  for  the  bacilli  are 
found  in  the  walls  of  the  intestines.  But  it  is 
not  a  proper  parasite,  and  the  fatal  disease  it 


THE   STORY  OF  GERM   LIFE. 


produces  is  the  result  of  the  absorption  of  the 

poisons  secreted  in  the  intestines. 

It  is  but  a  step  from  this  to  the  true  parasites. 

Typhoid  fever,  for  example,  is  a  disease  produced 

by  bacteria  which  grow  in  the  intestines,  but 
which  also  invade  the  tissues 
more  extensively  than  the 
cholera  germs  (Fig.  30).  They 
do  not  invade  the  body  gen- 
erally, however,  but  become 
somewhat  localized  in  special 
glands  like  the  liver,  the 
spleen,  etc.  Even  here  they 
do  not  appear  to  find  a  very 
favourable  condition,  for  they 
do  not  grow  extensively  in 
these  places.  They  are  likely 
to  be  found  in  the  spleen  in 
small  groups  or  centres,  but 
stained,  showing  the  not  generally  distributed 
characteristic  form  in  through  it.  Wherever  they 

cultures ;   b,    Stained  i  •,  • 

to  show  the  flageiia.  grow  they  produce  poison, 
which  has  been  called  typho 
toxine,  and  it  is  this  poison  chiefly  which  gives 
rise  to  the  fever. 

Quite  a  considerable  number  of  the  patho- 
genic germs  are,  like  the  typhoid  bacillus,  more 
or  less  confined  to  special  places.  Instead  of 
distributing  themselves  through  the  body  after 
they  find  entrance,  they  are  restricted  to  special 
organs.  The  most  common  example  of  a  para- 
site of  this  sort  is  the  tuberculosis  bacillus,  the 
cause  of  consumption,  scrofula,  white  swelling, 
lupus,  etc.  (Fig.  31).  Although  this  bacillus  is 
very  common  and  is  able  to  attack  almost  any 
organ  in  the  body,  it  is  usually  very  restricted  in 


PARASITIC   BACTERIA. 


137 


growth.  It  may  become  localized  in  a  small 
gland,  a  single  joint,  a  small  spot  in  the  lungs,  or 
in  the  glands  of  the  mesentery,  the  other  parts 
of  the  body  remaining  free  from  infection.  Not 
infrequently  the  whole  trouble  is  thus  confined 


FIG.  31. — Tuberculosis  bacillus :  a,  As  seen  in  lung  tissue  ;  b, 
More  magnified  ;  c,  As  sometimes  seen  in  sputum  of  con- 
sumptive patients. 

to  such  a  small  locality  that  nothing  serious  re- 
sults. But  in  other  instances  the  bacilli  may  after 
a  time  slowly  or  rapidly  distribute  themselves 
from  these  centres,  attacking  more  and  more  of 
the  body  until  perhaps  fatal  results  follow  in  the 
end.  This  disease  is  therefore  commonly  of  very 
slow  progress. 

Again,  we  have  still  other  parasites  which  are 
not  thus  confined,  but  which,  as  soon  as  they 
enter  the  body,  produce  a  general  infection,  at- 
tacking the  blood  and  perhaps  nearly  all  tissues 
simultaneously.  The  most  typical  example  of 
this  sort  is  anthrax  or  malignant  pustule,  a  disease 
fortunately  rare  in  man  (Fig.  32).  Here  the 
bacilli  multiply  in  the  blood,  and  very  soon  a 
general  and  fatal  infection  of  the  whole  body 
arises,  resulting  from  the  abundance  of  the  ba- 


138  THE  STORY  OF  GERM   LIFE. 

cilli  everywhere.     Some  of  the  obscure  diseases 
known  as  blood  poisoning  appear  to  be  of  the  same 

general  nature, 
these  diseases  re- 
sulting from  a  very 
general  invasion  of 
the  whole  body  by 
certain  pathogenic 
bacteria. 

In  general,  then, 
we  see  that  the  so- 
called  germ  diseas- 
es result  from  the 

FIG.  ^.-Anthrax  bacillus  (splenic      <*Ctj°n       rUP°n  .    the 

fever).  body     of     poisons 

produced  by  bac- 
terial growth.  Differences  in  the  nature  of  these 
poisons  produce  differences  in  the  character  of 
the  disease,  and  differences  in  the  parasitic  pow- 
ers of  the  different  species  of  bacteria  produce 
wide  differences  in  the  course  of  the  diseases  and 
their  relation  to  external  phenomena. 


WHAT    DISEASES    ARE    DUE    TO    BACTERIA? 

It  is,  of  course,  an  extremely  important  matter 
to  determine  to  what  extent  human  diseases  are 
caused  by  bacteria.  It  is  not  easy,  nor  indeed 
possible,  to  do  this  to-day  with  accuracy.  It  is 
no  easy  matter  to  prove  that  any  particular  dis- 
ease is  caused  by  bacteria.  To  do  this  it  is  neces- 
sary to  find  some  particular  bacterium  present  in 
all  cases  of  the  disease ;  to  find  some  method  of 
getting  it  to  grow  outside  the  body  in  culture 
media;  to  demonstrate  its  absence  in  healthy  ani- 
mals, or  healthy  human  individuals  if  it  be  a  hu- 


PARASITIC   BACTERIA.  139 

man  disease ;  and,  finally,  to  reproduce  the  disease 
in  healthy  animals  by  inoculating  them  with  the 
bacterium.  All  of  these  steps  of  proof  present 
difficulties,  but  especially  the  last  one.  In  the 
study  of  animals  it  is  comparatively  easy  to  re- 
produce a  disease  by  inoculation.  But  experi- 
ments upon  man  are  commonly  impossible,  and 
in  the  case  of  human  diseases  it  is  frequently 
very  difficult  or  impossible  to  obtain  the  final 
test  of  the  matter.  After  finding  a  specific  bac- 
terium associated  with  a  disease,  it  is  usually  pos- 
sible to  experiment  with  it  further  upon  animals 
only.  But  some  human  diseases  do  not  attack 
animals,  and  in  the  case  of  diseases  that  may  be 
given  to  animals  it  is  frequently  uncertain  wheth- 
er the  disease  produced  in  the  animal  by  such  in- 
oculation is  identical  with  the  human  disease  in 
question,  owing  to  the  difference  of  symptoms  in 
the  different  animals.  As  a  consequence,  the  proof 
of  the  germ  nature  of  different  diseases  varies  all 
the  way  from  absolute  demonstration  to  mere 
suspicion.  To  give  a  complete  and  correct  list 
of  the  diseases  caused  by  bacteria,  or  to  give  a 
list  of  the  bacteria  species  pathogenic  to  man,  is 
therefore  at  present  impossible. 

The  difficulty  of  giving  such  a  list  is  rendered 
greater  from  the  fact  that  we  have  in  recent  years 
learned  that  the  same  species  of  pathogenic  bac- 
terium may  produce  different  results  under  differ- 
ent conditions.  When  the  subject  of  germ  dis- 
ease was  first  studied  and  the  connection  between 
r  bacteria  and  disease  was  first  demonstrated,  it 
was  thought  that  each  particular  species  of 
pathogenic  bacteria  produced  a  single  definite 
disease ;  and  conversely,  each  germ  disease  was 
supposed  to  have  its  own  definite  species  of  bac- 


140  THE  STORY  OF  GERM   LIFE. 

terium  as  its  cause.  Recent  study  has  shown, 
however,  that  this  is  not  wholly  true.  It  is  true 
that  some  diseases  do  have  such  a  definite  rela- 
tion to  definite  bacteria.  The  anthrax  germ,  for 
example,  will  always  produce  anthrax,  no  matter 
where  or  how  it  is  inoculated  into  the  body.  So, 
also,  in  quite  a  number  of  other  cases  distinct 
specific  bacteria  are  associated  with  distinct  dis- 
eases. But,  on  the  other  hand,  there  are  some 
pathogenic  bacteria  which  are  not  so  definite  in 
their  action,  and  produce  different  results  in  ac- 
cordance with  circumstances,  the  effect  varying 
both  with  the  organ  attacked  and  with  the  condi- 
tion of  the  individual.  For  instance,  a  consider- 
able number  of  different  types  of  blood  poison- 
ing, septic czmia,  py&mia,  gangrene,  inflammation  of 
wounds,  or  formation  of  pus  from  slight  skin 
wounds — indeed,  a  host  of  miscellaneous  trou- 
bles, ranging  all  the  way  from  a  slight  pus  forma- 
tion to  a  violent  and  severe  blood  poisoning — all 
appear  to  be  caused  by  bacteria,  and  it  is  impos- 
sible to  make  out  any  definite  species  associated 
with  the  different  types  of  these  troubles.  There 
are  three  common  forms  of  so-called  pus  cocci, 
and  these  are  found  almost  indiscriminately  with 
various  types  of  inflammatory  troubles.  More- 
over, these  species  of  bacteria  are  found  with  al- 
most absolute  constancy  in  and  around  the  body, 
even  in  health.  They  are  on  the  clothing,  on  the 
skin,  in  the  mouth  and  alimentary  canal.  Here 
they  exist,  commonly  doing  no  harm.  They  have, 
however,  the  power  of  doing  injury  if  by  chance 
they  get  into  wounds.  But  their  power  of  doing 
injury  varies  both  with  the  condition  of  the  indi- 
vidual and  with  variations  in  the  bacteria  them- 
selves. If  the  individual  is  in  a  good  condition 


PARASITIC   BACTERIA.  141 

of  health  these  bacteria  have  little  power  of  in- 
juring him  even  when  they  do  get  into  such 
wounds,  while  at  times  of  feeble  vitality  they 
may  do  much  more  injury,  and  take  the  occasion 
of  any  little  cut  or  bruise  to  enter  under  the  skin 
and  give  rise  to  inflammation  and  pus.  Some 
people  will  develop  slight  abscesses  or  slight  in- 
flammations whenever  the  skin  is  bruised,  while 
with  others  such  bruises  or  cuts  heal  at  once 
without  trouble.  Both  are  doubtless  subject  to 
the  same  chance  of  infection,  but  the  one  resists, 
while  the  other  does  not.  In  common  parlance, 
we  say  that  such  a  tendency  to  abscesses  indi- 
cates a  bad  condition  of  the  blood — a  phrase 
which  means  nothing.  Further,  we  find  that  the 
same  species  of  bacterium  may  have  varying 
powers  of  producing  disease  at  different  times. 
Some  species  are  universal  inhabitants  of  the 
alimentary  canal  and  are  ordinarily  harmless, 
while  under  other  conditions  of  unknown  char- 
acter they  invade  the  tissues  and  give  rise  to  a 
serious  and  perhaps  fatal  disease.  We  may  thus 
recognise  some  bacteria  which  may  be  compared 
to  foreign  invaders,  while  others  are  domestic 
enemies.  The  former,  like  the  typhoid  bacillus, 
always  produce  trouble  when  they  succeed  in 
entering  the  body  and  finding  a  foothold.  The 
latter,  like  the  normal  intestinal  bacilli,  are  al- 
ways present  but  commonly  harmless,  only  under 
special  conditions  becoming  troublesome.  All 
this  shows  that  there  are  other  factors  in  deter- 
mining the  course  of  a  disease,  or  even  the  exist- 
ence of  a  disease,  than  the  simple  presence  of  a 
peculiar  species  of  pathogenic  bacterium. 

From  the  facts  just  stated  it  will  be  evident 
that  any  list  of  germ  diseases  will  be  rather  un- 


142  THE   STORY  OF  GERM   LIFE. 

certain.  Still,  the  studies  of  the  last  twenty  years 
or  more  have  disclosed  some  definite  relations  of 
bacteria  and  disease,  and  a  list  of  the  diseases 
more  or  less  definitely  associated  with  distinct 
species  of  bacteria  is  of  interest.  Such  a  list, 
including  only  well-known  diseases,  is  as  follows  : 

Name  of  disease.  Name  of  bacterium  producing  the  disease. 

Anthrax  (Malignant  pustule).    Bacillus  anthracis. 
Cholera.  Spirillum  cholera  asiaticce. 

Croupous  pneumonia.  Micrococcus pneumonia crouposce. 

Diphtheria.  Bacillus  diphtheria. 

Glanders.  Bacillus  mallei. 

Gonorrhoea.  Micrococcus  gonorrhoea. 

Influenza.  Bacillus  of  influenza. 

Leprosy.  Bacillus  lepra. 

Relapsing  fever.  Spirillum  Obermeieri. 

Tetanus  (lockjaw).  Bacillus  tetani. 

Tuberculosis  (including  con- 
sumption, scrofula,  etc.)        Bacillus  tuberculosis. 
Typhoid  fever.  Bacillus  typhi  abdominalis. 

Various  wound  infections,  including  septiccemia, 
fycemia,  acute  abscesses,  ulcers,  erysipelas,  etc.,  are  pro- 
duced by  a  few  forms  of  micrococci,  resembling 
each  other  in  many  points  but  differing  slightly. 
They  are  found  almost  indiscriminately  in  any  of 
these  wound  infections,  and  none  of  them  appears 
to  have  any  definite  relation  to  any  special  form 
of  disease  unless  it  be  the  micrococcus  of  erysip- 
elas. The  common  pus  micrococci  are  grouped 
under  three  species,  Staphylococcus  pyogenes  aureus, 
Staphylococcus  pyogenes,  and  Streptococcus  pyogenes. 
These  three  are  the  most  common,  but  others  are 
occasionally  found. 

In  addition  to  these,  which  may  be  regarded  as 
demonstrated,  the  following  diseases  are  with 
more  or  less  certainty  regarded  as  caused  by  dis- 
tinct specific  bacteria :  Bronchitis,  endocarditis, 


PARASITIC   BACTERIA.  143 

measles,  whooping-cough,  peritonitis,  pneumonia, 
syphilis. 

Still  another  list  might  be  given  of  diseases 
whose  general  nature  indicates  that  they  are 
caused  by  bacteria,  but  in  connection  with  which 
no  distinct  bacterium  has  yet  been  found.  As 
might  be  expected  also,  a  larger  list  of  animal 
diseases  has  been  demonstrated  to  be  caused  by 
these  organisms.  In  addition,  quite  a  number 
of  species  of  bacteria  have  been  found  in  such 
material  as  faeces,  putrefying  blood,  etc.,  which 
have  been  shown  by  experiment  to  be  capable  of 
producing  diseases  in  animals,  but  in  regard  to 
which  we  have  no  evidence  that  they  ever  do 
produce  actual  disease  under  any  normal  con- 
ditions. These  may  contribute,  perhaps,  to  the 
troubles  arising  from  poisonous  foods,  but  can 
not  be  regarded  as  disease  germs  proper. 

VARIABILITY    OF    PATHOGENIC    POWERS. 

As  has  already  been  stated,  our  ideas  of  the 
relation  of  bacteria  to  disease  have  undergone 
quite  a  change  since  they  were  first  formulated, 
and  we  recognise  other  factors  influencing  dis- 
ease besides  the  actual  presence  of  the  bac- 
terium. These  we  may  briefly  consider  under 
two  heads,  viz.,  variation  in  the  bacterium,  and 
variation  in  the  susceptibility  of  the  individual. 
The  first  will  require  only  a  brief  consideration. 

That  the  same  species  of  pathogenic  bacteria 
at  different  times  varies  in  its  powers  to  produce 
disease  has  long  been  known.  Various  con- 
ditions are  known  to  affect  thus  the  virulence  of 
bacteria.  The  bacillus  which  is  supposed  to  give 
rise  to  pneumonia  loses  its  power  to  produce  the 


144  THE   STORY  OF  GERM   LIFE. 

disease  after  having  been  cultivated  for  a  short 
time  in  ordinary  culture  media  in  the  laboratory. 
This  is  easily  understood  upon  the  suggestion 
that  it  is  a  parasitic  bacillus  and  does  not  thrive 
except  under  parasitic  conditions.  Its  patho- 
genic powers  can  sometimes  be  restored  by  pass- 
ing it  again  through  some  susceptible  animal. 
One  of  the  most  violent  pathogenic  bacteria  is 
that  which  produces  anthrax,  but  this  loses  its 
pathogenic  powers  if  it  is  cultivated  for  a  con- 
siderable period  at  a  high  temperature.  The 
micrococcus  which  causes  fowl  cholera  loses  its 
power  if  it  be  cultivated  in  common  culture  media, 
care  being  taken  to  allow  several  days  to  elapse 
between  the  successive  inoculations  into  new 
culture  flasks.  Most  pathogenic  bacteria  can 
in  some  way  be  so  treated  as  to  suffer  a  dimi- 
nution or  complete  loss  of  their  powers  of  pro- 
ducing a  fatal  disease.  On  the  other  hand,  other 
conditions  will  cause  an  increase  in  the  virulence 
of  a  pathogenic  germ.  The  virus  which  produces 
hydrophobia  is  increased  in  violence  if  it  is 
inoculated  into  a  rabbit  and  subsequently  taken 
from  the  rabbit  for  further  inoculation.  The 
fowl  cholera  micrococcus,  which  has  been  weak- 
ened as  just  mentioned,  may  be  restored  to  its 
original  violence  by  inoculating  it  into  a  small 
bird,  like  a  sparrow,  and  inoculating  a  second 
bird  from  this.  A  few  such  inoculations  will 
make  it  as  active  as  ever.  These  variations 
doubtless  exist  among  the  species  in  Nature  as 
well  as  in  artificial  cultures.  The  bacteria 
which  produce  the  various  wound  infections  and 
abscesses,  etc.,  appear  to  vary  under  normal  con- 
ditions from  a  type  capable  of  producing  violent 
and  fatal  blood  poisoning  to  a  type  producing 


PARASITIC   BACTERIA.  145 

only  a  simple  abscess,  or  even  to  a  type  that  is 
entirely  innocuous.  It  is  this  factor,  doubtless, 
which  in  a  large  measure  determines  the  severity 
of  any  epidemic  of  a  bacterial  contagious  dis- 
ease. 


SUSCEPTIBILITY    OF    THE    INDIVIDUAL. 

The  very  great  modification  of  our  early 
views  has  affected  our  ideas  as  to  the  power 
which  individuals  have  of  resisting  the  invasion 
of  pathogenic  bacteria.  It  has  from  the  first 
been  understood  that  some  individuals  are  more 
susceptible  to  disease  than  others,  and  in  attempt- 
ing to  determine  the  significance  of  this  fact 
many  valuable  and  interesting  discoveries  have 
been  made.  After  the  exposure  to  the  disease 
there  follows  a  period  of  some  length  in  which 
there  are  no  discernible  effects.  This  is  followed 
by  the  onset  of  the  disease  and  its  development 
to  a  crisis,  and,  if  this  be  passed,  by  a  recovery. 
The  general  course  of  a  germ  disease  is  divided 
into  three  stages:  the  stage  of  incubation,  the 
development  of  the  disease,  and  the  recovery.  The 
susceptibility  of  the  body  to  a  disease  may  be 
best  considered  under  the  three  heads  of  Inva- 
sion, Resistance,  Recovery. 

Means  of  Invasion. — In  order  that  a  germ  dis- 
ease should  arise  in  an  individual,  it  is  first  ne- 
cessary that  the  special  bacterium  which  causes 
the  disease  should  get  into  the  body.  There 
are  several  channels  through  which  bacteria  can 
thus  find  entrance  ;  these  are  through  the 
mouth,  through  the  nose,  through  the  skin,  and 
occasionally  through  excretory  ducts.  Those 
which  come  through  the  mouth  come  with  the 


146  THE  STORY  OF  GERM   LIFE. 

food  or  drink  which  we  swallow  ;  those  which 
enter  through  the  nose  must  be  traced  to  the  air; 
and  those  which  enter  through  the  skin  come  in 
most  cases  through  contact  with  some  infected 
object,  such  as  direct  contact  with  the  body  of 
an  infected  person  or  his  clothing  or  some  objects 
he  has  handled,  etc.  Occasionally,  perhaps,  the 
bacteria  may  get  into  the  skin  from  the  air,  but 
this  is  certainly  uncommon  and  confined  to  a  few 
diseases.  There  are  here  two  facts  of  the  utmost 
importance  for  every  one  to  understand :  first, 
that  the  chance  of  disease  bacteria  being  carried 
to  us  through  the  air  is  very  slight  and  confined 
to  a  few  diseases,  such  as  smallpox,  tuberculo- 
sis, scarlet  fever;  etc.,  and,  secondly,  that  the  un- 
injured skin  and  the  uninjured  mucous  membrane 
also  is  almost  a  sure  protection  against  the  in- 
vasion of  the  bacteria.  If  the  skin  is  whole, 
without  bruises  or  cuts,  bacteria  can  seldom,  if 
ever,  find  passage  through  it.  These  two  facts 
are  of  the  utmost  importance,  since  of  all  sources 
of  infection  we  have  the  least  power  to  guard 
against  infection  through  the  air,  and  since  of  all 
means  of  entrance  we  can  guard  the  skin  with 
the  greatest  difficulty.  We  can  easily  render 
food  free  from  pathogenic  bacteria  by  heating  it. 
The  material  we  drink  can  similarly  be  rendered 
harmless,  but  we  can  not  by  any  known  means 
avoid  breathing  air,  nor  is  there  any  known 
method  of  disinfecting  the  air,  and  it  is  impos- 
sible for  those  who  have  anything  to  do  with 
sick  persons  to  avoid  entirely  having  contact 
either  with  the  patient  or  with  infected  clothing 
or  utensils. 

From  the  facts  here  given  it  will  be  seen  that 
the  individual's  susceptibility  to  disease  produced 


PARASITIC   BACTERIA.  147 

by  parasitic  bacteria  will  depend  upon  his  habits 
of  cleanliness,  his  care  in  handling  infectious 
material,  or  care  in  cleansing  the  hands  after  such 
handling,  upon  his  habit  of.  eating  food  cooked 
or  raw,  and  upon  the  condition  of  his  skin  and 
mucous  membranes,  since  any  kind  of  bruises 
will  increase  susceptibility.  Slight  ailments, 
such  as  colds,  which  inflame  the  mucous  mem- 
brane, will  decrease  its  resisting  power  and  ren- 
der the  individual  more  susceptible  to  the  entrance 
of  any  pathogenic  germs  should  they  happen  to 
be  present.  Sores  in  the  mouth  or  decayed  teeth 
may  in  the  same  way  be  prominent  factors  in  the 
individual's  susceptibility.  Thus  quite  a  number 
of  purely  physical  factors  may  contribute  to  an 
individual's  susceptibility. 

Resisting  Power  of  the  Body. — Even  after  the 
bacteria  get  into  the  body  it  is  by  no  means  cer- 
tain that  they  will  give  rise  to  disease,  for  they 
have  now  a  battle  to  fight  before  they  can  be  sure 
of  holding  their  own.  It  is  now,  indeed,  that  the 
actual  conflict  between  the  powers  of  the  body 
and  these  microscopic  invaders  begins.  After 
they  have  found  entrance  into  the  body  the  bac- 
teria have  arrayed  against  them  strong  resisting 
forces  of  the  human  organism,  endeavouring  to 
destroy  and  expel  them.  Many  of  them  are  rapid- 
ly killed,  and  sometimes  they  are  all  destroyed 
without  being  able  to  gain  a  foothold.  In  such 
cases,  of  course,  no  trouble  results.  In  other 
cases  the  body  fails  to  overcome  the  powers  of 
the  invaders  and  they  eventually  multiply  rapidly. 
In  this  struggle  the  success  of  the  invaders  is  not 
necessarily  a  matter  of  numbers.  They  are  sim- 
ply struggling  to  gain  a  position  in  the  body,  where 
they  can  feed  and  grow.  A  few  individuals  may 


148  THE  STORY  OF  GERM   LIFE. 

be  entirely  sufficient  to  seize  such  a  foothold,  and 
then  these  by  multiplying  may  soon  become  in- 
definitely numerous.  To  protect  itself,  therefore, 
the  human  body  must  destroy  every  individual 
bacterium,  or  at  least  render  them  all  incapa- 
ble of  growth.  Their  marvellous  reproductive 
powers  give  the  bacteria  an  advantage  in  the  bat- 
tle. On  the  other  hand,  it  takes  time  even  for 
these  rapidly  multiplying  beings  to  become  suf- 
ficiently numerous  to  do  injury.  There  is  thus  an 
interval  after  their  penetration  into  the  body 
when  these  invaders  are  weak  in  numbers.  Dur- 
ing this  interval — the  period  of  incubation — the 
body  may  organize  a  resistance  sufficient  to  ex- 
pel them. 

We  do  not  as  yet  thoroughly  understand  the 
forces  which  the  human  organism  is  able  to  array 
against  these  invading  foes.  Some  of  its  meth- 
ods of  defence  are,  however,  already  intelligible 
to  us,  and  we  know  enough,  at  all  events,  to  give 
us  an  idea  of  the  intensity  of  the  conflict  that  is 
going  on,  and  of  the  vigorous  and  powerful  forces 
which  the  human  organism  is  able  to  bring  against 
its  invading  enemies. 

In  the  first  place,  we  notice  that  a  majority  of 
bacteria  are  utterly  unable  to  grow  in  the  human 
body  even  if  they  do  find  entrance.  There  are 
known  to  bacteriologists  to-day  many  hundreds, 
even  thousands  of  species,  but  the  vast  majority 
of  these  find  in  .the  human  tissues  conditions  so 
hostile  to  their  life  that  they  are  utterly  unable  to 
grow  therein.  Human  flesh  or  human  blood  will 
furnish  excellent  food  for  them  if  the  individual 
be  dead,  but  living  human  flesh  and  blood  in  some 
way  exerts  a  repressing  influence  upon  them  which 
is  fatal  to  the  growth  of  a  vast  majority  of  spe- 


PARASITIC   BACTERIA.  149 

cies.  Some  few  species,  however,  are  not  thus 
destroyed  by  the  hostile  agencies  of  the  tissues 
of  the  animal,  but  are  capable  of  growing  and 
multiplying  in  the  living  body.  These  alone  are 
what  constitute  the  pathogenic  bacteria,  since,  of 
course,  these  are  the  only  bacteria  which  can  pro- 
duce disease  by  growing  in  the  tissues  of  an  ani- 
mal. The  fact  that  the  vast  majority  of  bacteria 
can  not  grow  in  the  living  organism  shows  clearly 
enough  that  there  are  some  conditions  existing  in 
the  living  tissue  hostile  to  bacterial  life.  There 
can  be  little  doubt,  moreover,  that  it  is  these  same 
hostile  conditions,  which  enable  the  body  to  resist 
the  attack  of  the  pathogenic  species  in  cases 
where  resistance  is  successfully  made. 

What  are  the  forces  arrayed  against  these  in- 
vaders ?  The  essential  nature  of  the  battle  ap- 
pears to  be  a  production  of  poisons  and  counter 
poisons.  It  appears  to  be  an  undoubted  fact  that 
the  first  step  in  repelling  these  bacteria  is  to  flood 
them  with  certain  poisons  which  check  their 
growth.  In  the  blood  and  lymph  of  man  and 
other  animals  there  are  present  certain  products 
which  have  a  direct  deleterious  influence  upon  the 
growth  of  micro-organisms.  The  existence  of 
these  poisons  is  undoubted,  many  an  experiment 
having  directly  attested  to  their  presence  in  the 
blood  of  animals.  Of  their  nature  we  know  very 
little,  but  of  their  repressing  influence  upon  bac- 
terial growth  we  are  sure.  They  have  been  named 
alexines,  and  they  are  produced  in  the  living  tis- 
sue, although  as  to  the  method  of  their  pro- 
duction we  are  in  ignorance.  By  the  aid  of 
these  poisons  the  body  is  able  to  prevent  the 
growth  of  the  vast  majority  of  bacteria  which 
get  into  its  tissues.  Ordinary  micro-organisms 


150  THE   STORY  OF  GERM   LIFE. 

are  killed  at  once,  for  these  alexines  act  as  anti- 
septics, and  common  bacteria  can  no  more  grow 
in  the  living  body  than  they  could  in  a  solution 
containing  other  poisons.  Thus  the  body  has  a 
perfect  protection  against  the  majority  of  bac- 
teria. The  great  host  of  species  which  are  found 
in  water,  milk,  air,  in  our  mouths  or  clinging  to 
our  skin,  and  which  are  almost  omnipresent  in 
Nature,  are  capable  of  growing  well  enough  in  or- 
dinary lifeless  organic  foods  ;  but  just  as  soon  as 
they  succeed  in  finding  entrance  into  living  human 
tissue  their  growth  is  checked  at  once  by  these 
antiseptic  agents  which  are  poured  upon  them. 
Such  bacteria  are  therefore  not  pathogenic  germs, 
and  not  sources  of  trouble  to  human  health. 

There  are,  on  the  other  hand,  a  few  species  of 
bacteria  which  may  be  able  to  retain  their  lodg- 
ment in  the  body  in  spite  of  this  attempt  of  the 
individual  to  get  rid  of  them.  These,  of  course, 
constitute  the  pathogenic  species,  or  so-called 
"disease  germs."  Only  such  species  as  can  over- 
come this  first  resistance  can  be  disease  germs, 
for  they  alone  can  retain  their  foothold  in  the 
body. 

But  how  do  these  species  overcome  the  poi- 
sons which  kill  the  other  harmless  bacteria  ? 
They,  as  well  as  the  harmless  forms,  find  these 
alexines  injurious  to  their  growth,  but  in  some 
way  they  are  able  to  counteract  the  poisons.  In 
this  general  discussion  of  poisons  we  are  dealing 
with  a  subject  which  is  somewhat  obscure,  but 
apparently  the  pathogenic  bacteria  are  able  to 
overcome  the  alexines  of  the  body  by  producing 
in  their  turn  certain  other  products  which  neu- 
tralize the  alexines,  thus  annulling  their  action. 
These  pathogenic  bacteria,  when  they  get  into 


PARASITIC   BACTERIA.  151 

the  body,  give  rise  at  once  to  a  group  of  bodies 
which  have  been  named  lysines.  These  lysines 
are  as  mysterious  to  us  as  the  alexines,  but  they 
neutralize  the  effect  of  the  alexines  and  thus 
overcome  the  resistance  the  body  offers  to  bac- 
terial growth.  The  invaders  can  now  multiply 
rapidly  enough  to  get  a  lasting  foothold  in  the 
body  and  then  soon  produce  the  abnormal  symp- 
toms which  we  call  disease.  Pathogenic  bacteria 
thus  differ  from  the  non-pathogenic  bacteria 
primarily  in  this  power  of  secreting  products 
which  can  neutralize  the  ordinary  effects  of  the 
alexines,  and  so  overcome  the  body's  normal  re- 
sistance to  their  parasitic  life. 

Even  if  the  bacteria  do  thus  overcome  the 
alexines  the  battle  is  not  yet  over,  for  the  indi- 
vidual has  another  method  of  defence  which  is 
now  brought  into  activity  to  check  the  growth  of 
the  invading  organisms.  This  second  method  of 
resistance  is  by  means  of  a  series  of  active  cells 
found  in  the  blood,  known  as  white  blood-cor- 
puscles (Fig.  33  #,  b).  They  are  minute  bits  of 
protoplasm  present  in  the  blood  and  lymph  in 
large  quantities.  They  are  active  cells,  capable 
of  locomotion  and  able  to  crawl  out  of  the  blood- 
vessels. Not  infrequently  they  are  found  to  take 
into  their  bodies  small  objects  with  which  they 
come  in  contact.  One  of  their  duties  is  thus  to  en- 
gulf minute  irritating  bodies  which  may  be  in  the 
tissues,  and  to  carry  them  away  for  excretion. 
They  thus  act  as  scavengers.  These  corpuscles 
certainly  have  some  agency  in  warding  off  the  at- 
tacks of  pathogenic  bacteria.  Very  commonly 
they  collect  in  great  numbers  in  the  region  of 
the  body  where  invading  bacteria  are  found.  Such 
invading  bacteria  exert  upon  them  a  strong  attrac- 


152  THE   STORY  OF   GERM   LIFE. 


-  33-  — White  blood  corpuscles  and  other  phagocytes  :  a,  A  sta- 
tionary form  ;  b,  Motile  form  ;  c,  Phagocyte  with  a  bacterium 
half  engulfed ;  d,  Phagocytes  containing  bacteria  either  dead 
or  alive  ;  e,  Phagocyte  loaded  with  bacteria. 


PARASITIC   BACTERIA.  153 

tion,  and  the  corpuscles  leave  the  blood-vessels 
and  sometimes  form  a  solid  phalanx  completely 
surrounding  the  invading  germs.  Their  collec- 
tion at  these  points  may  make  itself  seen  exter- 
nally by  the  phenomenon  we  call  inflammation. 

There  is  no  question  that  the  corpuscles  en- 
gage in  conflict  with  the  bacteria  when  they  thus 
surround  them.  There  has  been  not  a  little  dis- 
pute, however,  as  to  the  method  by  which  they 
carry  on  the  conflict.  It  has  been  held  by  some 
that  the  corpuscles  actually  take  the  bacteria  into 
their  bodies,  swallow  them,  as  it  were,  and  subse- 
quently digest  them  (Fig.  33  c,  d,  e).  This  idea 
gave  rise  to  the  theory  of  phagocytosis,  and  the 
corpuscles  were  consequently  named  phagocytes. 
The  study  of  several  years  has,  however,  made  it 
probable  that  this  is  not  the  ordinary  method  by 
which  the  corpuscles  destroy  the  bacteria.  Ac- 
cording to  our  present  knowledge  the  method  is 
a  chemical  one.  These  cells,  when  they  thus  col- 
lect in  quantities  around  the  invaders,  appear  to 
secrete  from  their  own  bodies  certain  injurious 
products  which  act  upon  the  bacteria  much  as  do 
the  alexines  already  mentioned.  These  new  bod- 
ies have  a  decidedly  injurious  effect  upon  the 
multiplying  bacteria ;  they  rapidly  check  their 
growth,  and,  acting  in  union  with  the  alexines, 
may  perhaps  entirely  destroy  them. 

After  the  bacteria  are  thus  killed,  the  white 
blood-corpuscles  may  load  themselves  with  their 
dead  bodies  and  carry  them  away  (Fig.  33  d,  e). 
Sometimes  they  pass  back  into  the  blood  stream 
and  carry  the  bacteria  to  various  parts  of  the 
body  for  elimination.  Not  infrequently  the  white 
corpuscles  die  in  the  contest,  and  then  may  ac- 
cumulate in  the  form  of  pus  and  make  their  way 


154  THE  STORY   OF   GERM   LIFE. 

through  the  skin  to  be  discharged  directly.  The 
battle  between  these  phagocytes  and  the  bacteria 
goes  on  vigorously.  If  in  the  end  the  phagocytes 
prove  too  strong  for  the  invaders,  the  bacteria 
are  gradually  all  destroyed,  and  the  attack  is  re- 
pelled. Under  these  circumstances  the  individual 
commonly  knows  nothing  of  the  matter.  This 
conflict  has  taken  place  entirely  without  any  con- 
sciousness on  his  part,  and  he  may  not  even  know 
that  he  has  been  exposed  to  the  attack  of  the 
bacteria.  In  other  cases  the  bacteria  prove  too 
strong  for  the  phagocytes.  They  multiply  too 
rapidly,  and  sometimes  they  produce  secretions 
which  actually  drive  the  phagocytes  away.  Com- 
monly, as  already  noticed,  the  corpuscles  are  at- 
tracted to  the  point  of  invasion,  but  in  some  cases, 
when  a  particularly  deadly  and  vigorous  species 
of  bacteria  invades  the  body,  the  secretions  pro- 
duced by  them  are  so  powerful  as  actually  to 
drive  the  corpuscles  away.  Under  these  circum- 
stances the  invading  hosts  have  a  chance  to  mul- 
tiply unimpeded,  to  distribute  themselves  over  the 
body,  and  the  disease  rapidly  follows  as  the  result 
of  their  poisoning  action  on  the  body  tissues. 

It  is  plain,  then,  that  the  human  body  is  not 
helpless  in  the  presence  of  the  bacteria  of  disease, 
but  that  it  is  supplied  with  powerful  resistant 
forces.  It  must  not  be  supposed,  however,  that 
the  outline  of  the  action  of  these  forces  just  given 
is  anything  like  a  complete  account  of  the  matter; 
nor  must  it  be  inferred  that  the  resistance  is  in  all 
respects  exactly  as  outlined.  The  subject  has  only 
recently  been  an  object  of  investigation,  and  we  are 
as  yet  in  the  dark  in  regard  to  many  of  the  facts. 
The  future  may  require  us  to  modify  to  some  ex- 
tent even  the  brief  outline  which  has  been  given. 


PARASITIC   BACTERIA.  155 

But  while  we  recognise  this  uncertainty  in  the  de- 
tails, we  may  be  assured  of  the  general  facts. 
The  living  body  has  some  very  efficacious  resist- 
ant forces  which  prevent  most  bacteria  from 
growing  within  its  tissues,  and  which  in  large 
measure  may  be  relied  upon  to  drive  out  the  true 
pathogenic  bacteria.  These  resistant  forces  are 
in  part  associated  with  the  productions  of  body 
poisons,  and  are  in  part  associated  with  the  active 
powers  of  special  cells  which  have  been  called 
phagocytes.  The  origin  of  the  poisons  and  the 
exact  method  of  action  of  the  phagocytes  we  may 
well  leave  to  the  future  to  explain. 

These  resisting  powers  of  the  body  will  vary 
with  conditions.  It  is  evident  that  they  are 
natural  powers,  and  they  will  doubtless  vary  with 
the  general  condition  of  vigour  of  the  individual. 
Robust  health,  a  body  whose  powers  are  strong, 
well  nourished,  and  vigorous,  will  plainly  furnish 
the  conditions  for  the  greatest  resistance  to  bac- 
terial diseases.  One  whose  bodily  activities  are 
weakened  by  poor  nutrition  can  offer  less  resist- 
ance. The  question  whether  one  shall  suffer 
from  a  germ  disease  is  not  simply  the  question 
whether  he  shall  be  exposed,  or  even  the  question 
whether  the  bacteria  shall  find  entrance  into  his 
body.  It  is  equally  dependent  upon  whether  he 
has  the  bodily  vigour  to  produce  alexinesin  proper 
quantity,  or  to  summon  the  phagocytes  in  suffi- 
cient abundance  and  vigour  to  ward  off  the  attack. 
We  may  do  much  to  prevent  disease  by  sanitation, 
which  aids  in  protecting  the  individual  from  at- 
tack ;  but  we  must  not  forget  that  the  other  half 
of  the  battle  is  of  equal  importance,  and  hence 
we  must  do  all  we  can  to  strengthen  the  resist- 
ing forces  of  the  organism. 


156  THE   STORY   OF  GERM   LIFE. 

RECOVERY    FROM    GERM    DISEASES. 

These  resisting  forces  are  not  always  sufficient 
to  drive  off  the  invaders.  The  organisms  may 
retain  their  hold  in  the  body  for  a  time  and 
eventually  break  down  the  resistance.  After  this 
they  may  multiply  unimpeded  and  take  entire 
possession  of  the  body.  As  they  become  more 
numerous  their  poisonous  products  increase  and 
begin  to  produce  direct  poisoning  effects  on  the 
body.  The  incubation  period  is  over  and  the  dis- 
ease comes  on.  The  disease  now  runs  its  course. 
It  becomes  commonly  more  and  more  severe  until 
a  crisis  is  reached.  Then,  unless  the  poisoning  is 
so  severe  that  death  occurs,  the  effects  pass  away 
and  recovery  takes  place. 

But  why  should  not  a  germ  disease  be  always 
fatal  ?  If  the  bacteria  thus  take  possession  of  the 
body  and  can  grow  there,  why  do  they  not  always 
continue  to  multiply  until  they  produce  sufficient 
poison  to  destroy  the  life  of  the  individual  ? 
Such  fatal  results  do,  of  course,  occur,  but  in  by 
far  the  larger  proportion  of  cases  recovery  finally 
takes  place. 

Plainly,  the  body  must  have  another  set  of, 
resisting  forces  which  is  concerned  in  the  final 
recovery.  Although  weakened  by  the  poisoning 
and  suffering  from  the  disease,  it  does  not  yield 
the  battle,  but  somewhat  slowly  organizes  a  new 
attack  upon  the  invaders.  For  a  time  the  multi- 
plying bacteria  have  an  unimpeded  course  and 
grow  rapidly ;  but  finally  their  further  increase  is 
checked,  their  vigour  impaired,  and  after  this  they 
diminish  in  numbers  and  are  finally  expelled  from 
the  body  entirely.  Of  the  nature  of  this  new  re- 
sistance but  little  is  yet  known.  We  notice,  in 


PARASITIC   BACTERIA.  157 

the  first  place,  that  commonly  after  such  a  recov- 
ery the  individual  has  decidedly  increased  resist- 
ance to  the  disease.  This  increased  resistance 
may  be  very  lasting,  and  may  be  so  considerable 
as  to  give  almost  complete  immunity  from  the 
disease  for  many  years,  or  for  life.  One  attack 
of  scarlet  fever  gives  the  individual  great  immu- 
nity for  the  future.  On  the  other  hand,  the  re- 
sistance thus  derived  may  be  very  temporary,  as 
in  the  case  of  diphtheria.  But  a  certain  amount 
of  resistance  appears  to  be  always  acquired. 
This  power  of  resisting  the  activities  of  the  para- 
sites seems  to  be  increased  during  the  progress 
of  the  disease,  and,  if  it  becomes  sufficient,  it 
finally  drives  off  the  bacteria  before  they  have 
produced  death.  After  this,  recovery  takes  place. 
To  what  this  newly  acquired  resisting  power  is 
due  is  by  no  means  clear  to  bacteriologists,  al- 
though certain  factors  are  already  known.  It 
appears  beyond  question  that  in  the  case  of  cer- 
tain diseases  the  cells  of  the  body  after  a  time 
produce  substances  which  serve  as  antidotes  to 
the  poisons  produced  by  the  bacteria  during  their 
growth  in  the  body — antitoxines.  In  the  case  of 
diphtheria,  for  instance,  the  germs  growing  in  the 
throat  produce  poisons  which  are  absorbed  by  the 
body  and  give  rise  to  the  symptoms  of  the  dis- 
ease;  but  after  a  time  the  body  cells  react,  and 
themselves  produce  a  counter  toxic  body  which 
neutralizes  the  poisonous  effect  of  the  diphtheria 
poison.  This  substance  has  been  isolated  from 
the  blood  of  animals  that  have  recovered  from  an 
attack  of  diphtheria,  and  has  been  called  diphthe- 
ria antitoxine.  But  even  with  this  knowledge  the 
recovery  is  not  fully  explained.  This  antitoxine 
neutralizes  the  effects  of  the  diphtheria  toxine, 


158  THE  STORY  OF  GERM   LIFE. 

and  then  the  body  develops  strength  to  drive  off 
the  bacteria  which  have  obtained  lodgment  in  the 
throat.  How  they  accomplish  this  latter  achieve- 
ment we  do  not  know  as  yet.  The  antitoxine 
developed  simply  neutralizes  the  effects  of  the 
toxine.  Some  other  force  must  be  at  work  to  get 
rid  of  the  bacteria,  a  force  which  can  only  exert 
itself  after  the  poisoning  effect  of  the  poison  is 
neutralized.  In  these  cases,  then,  the  recovery  is 
due,  first,  to  the  development  in  the  body  of  the 
natural  antidotes  to  the  toxic  poisons,  and,  second, 
to  some  other  unknown  force  which  drives  off  the 
parasites. 

These  facts  are  certainly  surprising.  If  one 
had  been  asked  to  suggest  the  least  likely  theory 
to  explain  recovery  from  disease,  he  could  hardly 
have  found  one  more  unlikely  than  that  the  body 
cells  developed  during  the  disease  an  antidote  to 
the  poison  which  the  disease  bacteria  were  pro- 
ducing. Nevertheless,  it  is  beyond  question  that 
such  antidotes  are  formed  during  the  course  of 
the  germ  diseases.  It  has  not  yet  been  shown  in 
all  diseases,  and  it  would  be  entirely  too  much  to 
claim  that  this  is  the  method  of  recovery  in  all 
cases.  We  may  say,  however,  in  regard  to  bacte- 
rial diseases  in  general,  that  after  the  bacteria  en- 
ter the  body  at  some  weak  point  they  have  first  a 
battle  to  fight  with  the  resisting  powers  of  the  body, 
which  appear  to  be  partly  biological  and  partly 
chemical.  These  resisting  powers  are  in  many 
cases  entirely  sufficient  to  prevent  the  bacteria 
from  obtaining  a  foothold.  If  the  invading  host 
overcome  the  resisting  powers,  then  they  begin 
to  multiply  rapidly,  and  take  possession  of  the 
body  or  some  part  of  it.  They  continue  to  grow 
until  either  the  individual  dies  or  something  oc- 


PARASITIC   BACTERIA.  159 

curs  to  check  their  growth.  After  the  individual 
develops  the  renewed  powers  of  checking  their 
growth,  recovery  takes  place,  and  the  individual 
is  then,  because  of  these  renewed  powers  of  re- 
sistance, immune  from  a  second  attack  of  the  dis- 
ease for  a  variable  length  of  time. 

This,  in  the  merest  outline,  represents  the  rela- 
tion of  bacterial  parasites  to  the  human  body. 
But  while  this  is  a  fair  general  expression  of  the 
matter,  it  must  be  recognised  that  different  dis- 
eases differ  much  in  their  relations,  and  no  general 
outline  will  apply  to  all.  They  differ  in  their 
method  of  attack  and  in  the  point  of  attack.  Not 
only  do  they  produce  different  kinds  of  poisons 
giving  rise  to  different  symptoms  of  poisoning  ; 
not  only  do  they  produce  different  results  in  dif- 
ferent animals ;  not  only  do  the  different  patho- 
genic species  differ  much  in  their  power  to  de- 
velop serious  disease,  but  the  different  species  are 
very  particular  as  to  what  species  of  animal  they 
attack.  Some  of  them  can  live  as  parasites  in 
man  alone;  some  can-live  as  parasites  upon  man 
and  the  mouse  and  a  few  other  animals;  some 
can  live  in  various  animals  but  not  in  man  ;  some 
appear  to  be  able  to  live  in  the  field  mouse,  but 
not  in  the  common  mouse ;  some  live  in  the  horse; 
some  in  birds,  but  not  in  warm-blooded  mammals ; 
while  others,  again,  can  live  almost  equally  well 
in  the  tissues  of  a  long  list  of  animals.  Those 
which  can  live  as  parasites  upon  man  are,  of 
course,  especially  related  to  human  disease,  and 
are  of  particular  interest  to  the  physician,  while 
those  which  live  in  animals  are  in  a  similar  way 
of  interest  to  veterinarians. 

Thus  we  see  that  parasitic  bacteria  show  the 
widest  variations.  They  differ  in  point  of  attack, 
ii 


160  THE  STORY  OF  GERM   LIFE. 

in  method  of  attack,  and  in  the  part  ot  the  body 
which  they  seize  upon  as  a  nucleus  for  growth. 
They  differ  in  violence  and  in  the  character  of  the 
poisons  they  produce,  as  well  as  in  their  power  of 
overcoming  the  resisting  powers  of  the  body. 
They  differ  at  different  times  in  their  powers  of 
producing  disease.  In  short,  they  show  such  a 
large  number  of  different  methods  of  action  that 
no  general  statements  can  be  made  which  will  ap- 
ply universally,  and  no  one  method  of  guarding 
against  them  or  in  driving  them  off  can  be  hoped 
to  apply  to  any  extended  list  of  diseases. 

DISEASES    CAUSED    BY    OTHER    ORGANISMS    THAN 
BACTERIA. 

Although  the  purpose  of  this  work  is  to  deal 
primarily  with  the  bacterial  world,  it  would  hardly 
be  fitting  to  leave  the  subject  without  some  refer- 
ence to  diseases  caused  by  organisms  which  do 
not  belong  to  the  group  of  bacteria.  While  most 
of  the  so-called  germ  diseases  are  caused  by  the 
bacteria  which  we  have  been  studying  in  the 
previous  chapters,  there  are  some  whose  inciting 
cause  is  to  be  found  among  organisms  belonging 
to  other  groups.  Some  of  these  are  plants  of  a 
higher  organization  than  bacteria,  but  others  are 
undoubtedly  microscopic  animals.  Their  life 
habits  are  somewhat  different  from  those  of 
bacteria,  and  hence  the  course  of  the  diseases  is 
commonly  different.  Of  the  diseases  thus  pro- 
duced by  microscopic  animals  or  by  higher  plants, 
one  or  two  are  of  importance  enough  to  deserve 
special  mention  here. 

Malaria. — The  most  important  of  these  dis- 
eases is  malaria  in  its  various  forms,  and  known 


PARASITIC   BACTERIA. 


161 


under  various  names — chills  and  fever,  autumnal 
fever,  etc.  This  disease,  so  common  almost 
everywhere,  has  been  studied  by  physicians  and 
scientists  for  a  long  time,  and  many  have  been 
the  causes  assigned  to  it.  At  one  time  it  was 
thought  to  be  the  result  of  the  growth  of  a  bacte- 
rium, and  a  distinct  bacillus  was  described  as  pro- 
ducing it.  It  has  finally  been  shown,  however, 
to  be  caused  by  a  microscopic  organism  belong- 
ing to  the  group  of  unicellular  animals,  and  some- 


FlG.  34. — Malarial  organism  :  Figs,  a  to  g  show  the  growth  of 
the  parasite  within  the  blood  corpuscle ;  o  is  the  organism  in 
all  cases ;  s,  the  spores.  Fig.  i  is  the  so-called  cresentic  body 
which  develops  through  Fig.  2,  into  the  flagellate  form,  shown 
at  3.  The  significance  of  i,  2,  and  3  are  not  known. 

what  closely  related  to  the  well-known  amoeba. 
This  organism  is  shown  in  Fig.  34.  The  whole 
history  of.the  malarial  organism  is  not  yet  known. 
The  following  statements  comprise  the  most  im- 
portant facts  known  in  regard  to  it,  and  its  rela- 
tion to  the  disease  in  man. 

Undoubtedly  the  malarial  germ  has  some 
home  outside  the  human  body,  but  it  is  not  yet 
very  definitely  known  what  this  external  home  is; 
nor  do  we  know  from  what  source  the  human  para- 


1 62  THE   STORY  OF   GERM    LIFE. 

site  is  derived.  It  appears  probable  that  water 
serves  in  some  cases  as  its  means  of  transference 
to  man,  and  air  in  other  cases.  From  some  ex- 
ternal source  it  gains  access  to  man  and  finds 
its  way  into  the  blood.  Here  it  attacks  the 
red  blood-corpuscles,  each  malarial  organism 
making  its  way  into  a  single  one  (Fig.  340). 
Here  it  now  grows,  increasing  in  size  at  the 
expense  of  the  substance  of  the  corpuscle 
(Fig.  34  a-f).  As  it  becomes  larger  it  becomes 
granular,  and  soon  shows  a  tendency  to  separate 
into  a  number  of  irregular  masses  (Fig.  34  f). 
Finally  it  breaks  up  into  many  minute  bodies 
called  spores  (Fig.  34^").  These  bodies  break  out 
of  the  corpuscle  and  for  a  time  live  a  free  life  in 
the  blood  (Fig.  34  ti).  After  a  time  they  make 
their  way  into  other  red  blood-corpuscles,  develop 
into  new  malarial  amoeboid  parasites,  and  repeat 
the  growth  and  sporulation.  This  process  can  ap- 
parently be  repeated  many  times  without  check. 

These  organisms  are  thus  to  be  regarded  as 
parasites  of  the  red  corpuscles.  It  is,  of  course, 
easy  to  believe  that  an  extensive  parasitism  and 
destruction  of  the  corpuscles  would  be  disastrous 
to  the  health  of  the  individual,  and  the  severity 
of  the  disease  will  depend  upon  the  extent  of  the 
parasitism.  Corresponding  to  this  life  history  of 
the  organism,  the  disease  malaria  is  commonly 
characterized  by  a  decided  intermittency,  periods 
of  chill  and  fever  alternating  with  periods  of  in- 
termission in  which  these  symptoms  are  abated. 
The  paroxysms  of  the  disease,  characterized  by 
the  chill,  occur  at  the  time  that  the  spores  are 
escaping  from  the  blood-corpuscles  and  floating 
in  the  blood.  After  they  have  again  found  their 
way  into  a  blood-corpuscle  the  fever  diminishes, 


PARASITIC    BACTERIA.  163 

and  during  their  growth  in  the  corpuscle  until 
the  next  sporulation  the  individual  has  a  rest 
from  the  more  severe  symptoms. 

There  appears  to  be  more  than  one  variety  of 
the  malarial  organism,  the  different  types  differ- 
ing in  the  length  of  time  it  takes  for  their  growth 
and  sporulation.  There  is  one  variety,  the  most 
common  one,  which  requires  two  days  for  its 
growth,  thus  giving  rise  to  the  paroxysm  of  the 
disease  about  once  in  forty-eight  hours  ;  another 
variety  appears  to  require  three  days  for  its 
growth ;  while  still  another  variety  appears  to  be 
decidedly  irregular  in  its  period  of  growth  and 
sporulation.  These  facts  readily  explain  some  of 
the  variations  in  the  disease.  Certain  other  ir- 
regularities appear  to  be  due  to  a  different  cause. 
More  than  one  brood  of  parasites  may  be  in  the 
blood  of  the  individual  at  the  same  time,  one 
producing  sporulation  at  one  time  and  another  at 
a  different  time.  Such  a  simultaneous  growth  of 
two  independent  broods  may  plainly  produce  al- 
most any  kind  of  modification  in  the  regularity  of 
the  disease. 

The  malarial  organism  appears  to  be  very 
sensitive  to  quinine,  a  very  small  quantity  being 
sufficient  to  kill  it.  Upon  this  point  depends  the 
value  of  quinine  as  a  medicine.  If  the  drug  be 
present  in  the  blood  at  the  time  when  the  spores 
are  set  free  from  the  blood-corpuscle,  they  are 
rapidly  killed  by  it  before  they  have  a  chance  to 
enter  another  corpuscle.  During  their  growth  in 
the  corpuscle  they  are  far  less  sensitive  to  qui- 
nine than  when  they  exist  in  the  free  condition  as 
spores,  and  at  this  time  the  drug  has  little  effect. 

The  malarial  organism  is  an  animal,  and  can 
not  be  cultivated  in  the  laboratory  by  any  arti- 


164  THE  STORY  OF  GERM   LIFE. 

ficial  method  yet  devised.  Its  whole  history  is 
therefore  not  known.  It  doubtless  has  some 
home  outside  the  blood  of  animals,  arid  very 
likely  it  may  pass  through  other  stages  of  a  meta- 
morphosis in  the  bodies  of  other  animals.  Most 
parasitic  animals  have  two  or  more  hosts  upon 
which  they  live,  alternating  from  one  to  the  other, 
and  that  such  is  the  case  with  the  malarial  para- 
site is  at  least  probable.  But  as  yet  bacteriolo- 
gists have  been  unable  to  discover  anything  very 
definite  in  regard  to  the  matter.  Until  we  can 
learn  something  in  regard  to  its  life  outside  the 
blood  of  man  we  can  do  little  in  the  way  of  devis- 
ing methods  to  avoid  it. 

Malaria  differs  from  most  germ  diseases  in  the 
fact  that  the  organisms  which  produce  it  are  not 
eliminated  from  the  body  in  any  way.  In  most 
germ  diseases  the  germs  are  discharged  from  the 
patient  by  secretions  or  excretions  of  some  kind, 
and  from  these  excretions  may  readily  find  their 
way  into  other  individuals.  The  malarial  organ- 
ism is  not  discharged  from  the  body  in  any  way, 
and  hence  is  not  contagious.  If  the  parasite  does 
pass  part  of  its  history  in  some  other  animal 
than  man,  there  must  be  some  means  by  which  it 
passes  from  man  to  its  other  host.  It  has  been 
suggested  that  some  of  the  insects  which  feed 
upon  human  blood  may  serve  as  the  second  host 
and  become  inoculated  when  feeding  upon  such 
blood.  This  has  been  demonstrated  with  start- 
ling success  in  regard  to  the  mosquito  (Anopheles), 
some  investigators  going  so  far  as  to  say  that  this 
is  the  only  way  in  which  the  disease  can  be  com- 
municated. 

Several  other  microscopic  animals  occur  as 
parasites  upon  man,  and  some  of  them  are  so 
definitely  associated  with  certain  diseases  as  to 


COMBATING   PARASITIC   BACTERIA.  165 

lead  to  the  belief  that  they  are  the  cause  of  these 
diseases.  The  only  one  of  very  common  occur- 
rence is  a  species  known  as  Amoeba  coli,  which  is 
found  in  cases  of  dysentery.  In  a  certain  type 
of  dysenterythis  organism  is  so  universally  found 
that  there  is  little  doubt  that  it  is  in  some  very 
intimate  way  associated  with  the  cause  of  the  dis- 
ease. Definite  proof  of  the  matter  is,  however, 
as  yet  wanting. 

On  the  side  of  plants,  we  find  that  several 
plants  of  a  higher  organization  than  bacteria  may 
become  parasitic  upon  the  body  of  man  and  pro- 
duce various  types  of  disease.  These  plants  be- 
long mostly  to  the  same  group  as  the  moulds, 
and  they  are  especially  apt  to  attack  the  skin. 
They  grow  in  the  skin,  particularly  under  the  hair, 
and  may  send  their  threadlike  branches  into  some 
of  the  subdermal  tissues.  This  produces  irrita- 
tion and  inflammation  of  the  skin,  resulting  in 
trouble,  and  making  sores  difficult  to  heal.  So 
long  as  the  plant  continues  to  grow,  the  sores,  of 
course,  can  not  be  healed,  and  when  the  organ- 
isms get  into  the  skin  under  the  hair  it  is  fre- 
quently difficult  to  destroy  them.  Among  the 
diseases  thus  caused  are  ringworm,  thrush,  alopecia, 
etc. 


CHAPTER   VI. 

METHODS    OF    COMBATING    PARASITIC    BACTERIA. 

THE  chief  advantage  of  knowing  the  cause  of 
disease  is  that  it  gives  us  a  vantage  ground  from 
which  we  may  hope  to  find  means  of  avoiding  its 
evils.  The  study  of  medicine  in  the  past  history 


1 66  THE  STORY  OF  GERM   LIFE. 

of  the  world  has  been  almost  purely  empirical, 
with  a  very  little  of  scientific  basis.  Great  hopes 
are  now  entertained  that  these  new  facts  will  place 
this  matter  upon  a  more  strictly  scientific  foun- 
dation. Certainly  in  the  past  twenty-five  years, 
since  bacteriology  has  been  studied,  more  has 
been  done  to  solve  problems  connected  with  dis- 
ease than  ever  before.  This  new  knowledge  has 
been  particularly  directed  toward  means  of  avoid- 
ing disease.  Bacteriology  has  thus  far  borne 
fruit  largely  in  the  line  of  preventive  medicine, 
although  to  a  certain  extent  also  along  the  line 
of  curative  medicine.  This  chapter  will  be  de- 
voted to  considering  how  the  study  of  bacteriol- 
ogy has  contributed  directly  and  indirectly  to 
our  power  of  combating  disease. 

PREVENTIVE    MEDICINE. 

In  the  study  of  medicine  in  the  past  centuries 
the  only  aim  has  been  to  discover  methods  of 
curing  disease  ;  at  the  present  time  a  large  and 
increasing  amount  of  study  is  devoted  to  the 
methods  of  preventing  disease.  Preventive  medi- 
cine is  a  development  of  the  last  few  years,  and 
is  based  almost  wholly  upon  our  knowledge  of 
bacteria.  This  subject  is  yearly  becoming  of 
more  importance.  Forewarned  is  forearmed,  and 
it  has  been  found  that  to  know  the  cause  of  a 
disease  is  a  long  step  toward  avoiding  it.  As 
some  of  our  contagious  and  epidemic  diseases 
have  been  studied  in  the  light  of  bacteriological 
knowledge,  it  has  been  found  possible  to  deter- 
mine not  only  their  cause,  but  also  how  infection 
is  brought  about,  and  consequently  how  conta- 
gion may  be  avoided.  Some  of  the  results  which 


COMBATING   PARASITIC   BACTERIA.  167 

have  grown  up  so  slowly  as  to  be  hardly  appre- 
ciated are  really  great  triumphs.  For  instance, 
the  study  of  bacteriology  first  led  us  to  suspect, 
and  then  demonstrated,  that  tuberculosis  is  a 
contagious  disease,  and  from  the  time  that  this 
was  thus  proved  there  has  been  a  slow,  but,  it  is 
hoped,  a  sure  decline  in  this  disease.  Bacterio- 
logical study  has  shown  that  the  source  of  chol- 
era infection  in  cases  of  raging  epidemics  is,  in 
large  part  at  least,  our  drinking  water ;  and  since 
this  has  been  known,  although  cholera  has  twice 
invaded  Europe,  and  has  been  widely  distributed, 
it  has  not  obtained  any  strong  foothold  or  given 
rise  to  any  serious  epidemic  except  in  a  few  cases 
where  its  ravages  can  be  traced  to  recognised 
carelessness.  It  is  very  significant  to  compare 
the  history  of  the  cholera  epidemics  of  the  past 
few  years  with  those  of  earlier  dates.  In  the  epi- 
demics of  earlier  years  the  cholera  swept  ruth- 
lessly through  communities  without  check.  In 
the  last  few  years,  although  it  has  repeatedly 
knocked  at  the  doors  of  many  European  cities,  it 
has  been  commonly  confined  to  isolated  cases, 
except  in  a  few  instances  where  these  facts  con- 
cerning the  relation  to  drinking  water  were  ig- 
nored. 

The  study  of  preventive  medicine  is  yet  in  its 
infancy,  but  it  has  already  accomplished  much. 
It  has  developed  modern  systems  of  sanitation, 
has  guided  us  in  the  building  of  hospitals,  given 
rules  for  the  management  of  the  sick-room  which 
largely  prevent  contagion  from  patient  to  nurse; 
it  has  told  us  what  diseases  are  contagious,  and  in 
what  way  ;  it  has  told  us  what  sources  of  conta- 
gion should  be  suspected  and  guarded  against, 
and  has  thus  done  very  much  to  prevent  the 


1 68  THE   STORY  OF  GERM   LIFE. 

spread  of  disease.  Its  value  is  seen  in  the  fact  that 
there  has  been  a  constant  decrease  in  the  death 
rate  since  modern  ideas  of  sanitation  began  to 
have  any  influence,  and  in  the  fact  that  our 
general  epidemics  are  less  severe  than  in  former 
years,  as  well  as  in  the  fact  that  more  people 
escape  the  diseases  which  were  in  former  times 
almost  universal. 

The  study  of  preventive  medicine  takes  into 
view  several  factors,  all  connected  with  the 
method  and  means  of  contagion.  They  are  the 
following : 

The  Source  of  Infectious  Material. — It  has  been 
learned  that  for  most  diseases  the  infectious  ma- 
terial comes  from  individuals  suffering  with  the 
disease,  and  that  except  in  a  few  cases,  like  ma- 
laria, we  must  always  look  to  individuals  suffering 
from  disease  for  all  sources  of  contagion.  It  is 
found  that  pathogenic  bacteria  are  in  all  these 
cases  eliminated  from  the  patient  in  some  way, 
either  from  the  alimentary  canal  or  from  skin  se- 
cretions or  otherwise,  and  that  any  nurse  with 
common  sense  can  have  no  difficulty  in  deter- 
mining in  what  way  the  infectious  material  is 
eliminated  from  her  patients.  When  this  fact  is 
known  and  taken  into  consideration  it  is  a  com- 
paratively easy  matter  to  devise  valuable  precau- 
tions against  distribution  of  such  material.  It  is 
thus  of  no  small  importance  to  remember  that  the 
simple  presence  of  bacteria  in  food  or  drink  is  of 
no  significance  unless  these  bacteria  have  come 
from  some  source  of  disease  infection. 

The  Method  of  Distribution. — The  bacteria  must 
next  get  from  the  original  source  of  the  disease  to 
the  new  susceptible  individual.  Bacteria  have  no 
independent  powers  of  distribution  unless  they 


COMBATING   PARASITIC   BACTERIA.  169 

be  immersed  in  liquids,  and  therefore  their  pas- 
sage from  individual  to  individual  must  be  a  pas- 
sive one.  They  are  readily  transferred,  however, 
by  a  number  of  different  means,  and  the  study  of 
these  means  is  aiding  much  in  checking  contagion 
Study  along  this  line  has  shown  that  the  means 
by  which  bacteria  are  carried  are  several.  First 
we  may  notice  food  as  a  distributor.  Food  may 
become  contaminated  by  infectious  material  in 
many  ways ;  for  example,  by  contact  with  sewage, 
or  with  polluted  water,  or  even  with  eating  uten- 
sils which  have  been  used  by  patients.  Water  is 
also  likely  to  be  contaminated  with  infectious 
material,  and  is  a  fertile  source  for  distributing 
typhoid  and  cholera.  Milk  may  become  contam- 
inated in  a  variety  of  ways,  and  be  a  source  of  dis- 
tributing the  bacteria  which  produce  typhoid 
fever,  tuberculosis,  diphtheria,  scarlet  fever,  and 
a  few  other  less  common  diseases.  Again,  in- 
fected clothing,  bedding,  or  eating  utensils  may 
be  taken  from  a  patient  and  be  used  by  another 
individual  without  proper  cleansing.  Direct  con- 
tact, or  contact  with  infected  animals,  furnishes 
another  method.  Insects  sometimes  carry  the 
bacteria  from  person  to  person,  and  in  some  dis- 
eases (tuberculosis,  and  perhaps  scarlet  fever  and 
smallpox)  we  must  look  to  the  air  as  a  distribu- 
tor of  the  infectious  material.  Knowledge  of 
these  facts  is  helping  to  account  for  multitudes 
of  mysterious  cases  of  infection,  especially  when 
we  combine  them  with  the  known  sources  of  con- 
tagious matter. 

Means  of  Invasion. — Bacteriology  has  shown  us 
that  different  species  of  parasitic  bacteria  have 
different  means  of  entering  the  body,  and  that 
each  must  enter  the  proper  place  in  order  to  get 


1 70  THE   STORY  OF  GERM   LIFE. 

a  foothold.  After  we  learn  that  typhoid  infec- 
tious material  must  enter  the  mouth  in  order  to 
produce  the  disease;  that  tuberculosis  may  find 
entrance  through  the  nose  in  breathing,  while 
types  of  blood  poisoning  enter  only  through 
wounds  or  broken  skin,  we  learn  at  once  funda- 
mental facts  as  to  the  proper  methods  of  meeting 
these  dangers.  We  learn  that  with  some  diseases 
care  exercised  to  prevent  the  swallowing  of  infec- 
tious material  is  sufficient  to  prevent  contagion, 
while  with  others  this  is  entirely  insufficient. 
When  all  these  facts  are  understood  it  is  almost 
always  perfectly  possible  to  avoid  contagion  ;  and 
as  these  facts  become  more  and  more  widely  known 
direct  contagion  is  sure  to  become  less  frequent. 

Above  all,  it  is  telling  us  what  becomes  of  the 
pathogenic  bacteria  after  being  eliminated  from 
the  body  of  the  patient ;  how  they  may  exist  for 
a  long  time  still  active  ;  how  they  may  lurk  in 
filth  or  water  dormant  but  alive,  or  how  they  may 
even  multiply  there.  Preventive  medicine  is  tell- 
ing us  how  to  destroy  those  thus  lying  in  wait  for 
a  chance  of  infection,  by  discovering  disinfect- 
ants and  telling  us  especially  where  and  when  to 
use  them.  It  has  already  taught  us  how  to  crush 
out  certain  forms  of  epidemics  by  the  proper 
means  of  destroying  bacteria,  and  is  lessening 
the  dangers  from  contagious  diseases.  In  short, 
the  study  of  bacteriology  has  brought  us  into  a 
condition  where  we  are  no  longer  helpless  in  the 
presence  of  a  raging  epidemic.  We  no  longer  sit 
in  helpless  dismay,  as  did  our  ancestors,  when  an 
epidemic  enters  a  community,  but,  knowing  their 
causes  and  sources,  set  about  at  once  to  remove 
them.  As  a  result,  severe  epidemics  are  becoming 
comparatively  short-lived. 


COMBATING  PARASITIC   BACTERIA.  171 

BACTERIA  IN  SURGERY. 

In  no  line  of  preventive  medicine  has  bacteri- 
ology been  of  so  much  value  and  so  striking  in 
its  results  as  in  surgery.  Ever  since  surgery  has 
been  practised  surgeons  have  had  two  difficulties 
to  contend  with.  The  first  has  been  the  shock 
resulting  from  the  operation.  This  is  dependent 
upon  the  extent  of  the  operation,  and  must  always 
be  a  part  of  a  surgical  operation.  The  second 
has  been  secondary  effects  following  the  operation. 
After  the  operation,  even  though  it  was  success- 
ful, there  were  almost  sure  to  arise  secondary 
complications  known  as  surgical  fever,  inflamma- 
tion, blood  poisoning,  gangrene,  etc.,  which  fre- 
quently resulted  fatally.  These  secondary  com- 
plications were  commonly  much  more  serious 
than  the  shock  of  the  operation,  and  it  used  to  be 
the  common  occurrence  for  the  patient  to  recover 
entirely  from  the  shock,  but  yield  to  the  fevers 
which  followed.  They  appeared  to  be  entirely 
unavoidable,  and  were  indeed  regarded  as  neces- 
sary parts  of  the  healing  of  the  wound.  Too  fre- 
quently it  appeared  that  the  greater  the  care  taken 
with  the  patient  the  more  likely  he  was  to  suffer 
from  some  of  these  troubles.  The  soldier  who 
was  treated  on  the  battlefield  and  nursed  in  an 
improvised  field  hospital  would  frequently  re- 
cover, while  the  soldier  who  had  the  fortune  to 
be  taken  into  the  regular  hospital,  where  greater 
care  was  possible,  succumbed  to  hospital  gangrene. 
All  these  facts  were  clearly  recognised,  but  the 
surgeon,  through  ignorance  of  their  cause,  was 
helpless  in  the  presence  of  these  inflammatory 
troubles,  and  felt  it  always  necessary  to  take  them 
into  consideration. 


172  THE  STORY  OF  GERM   LIFE. 

The  demonstration  that  putrefaction  and  de- 
cay were  caused  by  bacteria,  and  the  early  proof 
that  the  silkworm  disease  was  produced  by  a 
micro-organism,  led  to  the  suggestion  that  the  in- 
flammatory diseases  accompanying  wounds  were 
similarly  caused.  There  are  many  striking  sim- 
ilarities between  these  troubles  and  putrefaction, 
and  the  suggestion  was  an  obvious  one.  At  first, 
however,  and  for  quite  a  number  of  years,  it  was 
impossible  to  demonstrate  the  theory  by  finding 
the  distinct  species  of  micro-organisms  which  pro- 
duced the  troubles.  We  have  already  seen  that 
there  are  several  different  species  of  bacteria  which 
are  associated  with  this  general  class  of  diseases, 
but  that  no  specific  one  has  any  particular  relation 
to  a  definite  type  of  inflammation.  This  fact  made 
discoveries  in  this  connection  a  slow  matter  from 
the  microscopical  standpoint.  But  long  before 
this  demonstration  was  finally  reached  the  theory 
had  received  practical  application  in  the  form  of 
what  has  developed  into  antiseptic  or  aseptic 
surgery. 

Antiseptic  surgery  is  based  simply  upon  the 
attempt  to  prevent  the  entrance  of  bacteria  into 
the  surgical  wound.  It  is  assumed  that  if  these 
organisms  are  kept  from  the  wound  the  healing 
will  take  place  without  the  secondary  fevers  and 
inflammations  which  occur  if  they  do  get  a  chance 
to  grow  in  the  wound.  The  theory  met  with  de- 
cided opposition  at  first,  but  accumulating  facts 
demonstrated  its  value,  and  to-day  its  methods 
have  been  adopted  everywhere  in  the  civilized 
world.  As  the  evidence  has  been  accumulating, 
surgeons  have  learned  many  important  facts,  fore- 
most among  which  is  a  knowledge  of  the  common 
sources  from  which  the  infection  of  wounds  oc- 


COMBATING  PARASITIC   BACTERIA.  173 

curs.  At  first  it  was  thought  that  the  air  was  the 
great  source  of  infection,  but  the  air  bacteria  have 
been  found  to  be  usually  harmless.  It  has  ap- 
peared that  the  more  common  sources  are  the 
surgeon's  instruments,  or  his  hands,  or  the  cloth- 
ing or  sponges  which  are  allowed  to  come  in  con- 
tact with  the  wounds.  It  has  also  appeared  that 
the  bacteria  which  produce  this  class  of  troubles 
are  common  species,  existing  everywhere  and  uni- 
versally present  around  the  body,  clinging  to  the 
clothing  or  skin,  and  always  on  hand  to  enter  the 
wound  if  occasion  offers.  They  are  always  pres- 
ent, but  commonly  harmless.  They  are  not  for- 
eign invaders  like  the  more  violent  pathogenic 
species,  such  as  those  of  Asiatic  cholera,  but  may 
be  compared  to  domestic  enemies  at  hand.  It  is 
these  ever-present  bacteria  which  the  surgeon 
must  guard  against.  The  methods  by  which  he 
does  this  need  not  detain  us  here.  They  consist 
essentially  in  bacteriological  cleanliness.  The 
operation  is  performed  with  sterilized  instruments 
under  most  exacting  conditions  of  cleanliness. 

The  result  has  been  a  complete  revolution  in 
surgery.  As  the  methods  have  become  better 
understood  and  more  thoroughly  adopted,  the  in- 
stances of  secondary  troubles  following  surgical 
wounds  have  become  less  and  less  frequent  until 
they  have  practically  disappeared  in  all  simple 
cases.  To-day  the  surgeon  recognises  that  when 
inflammatory  troubles  of  this  sort  follow  simple 
surgical  wounds  it  is  a  testimony  to  his  careless- 
ness. The  skilful  surgeon  has  learned  that  with 
the  precautions  which  he  is  able  to  take  to-day 
he  has  to  fear  only  the  direct  effect  of  the  shock 
of  the  wound  and  its  subsequent  direct  influence; 
but  secondary  surgical  fevers,  blood  poisoning, 


174  THE   STORY  OF  GERM   LIFE. 

and  surgical  gangrene  need  not  be  taken  into  con- 
sideration at  all.  Indeed,  the  modern  surgeon 
hardly  knows  what  surgical  gangrene  is,  and  bac- 
teriologists have  had  practically  no  chance  to 
study  it.  Secondary  infections  have  largely  dis- 
appeared, and  the  surgeon  is  concerned  simply 
with  the  effect  of  the  wound  itself,  and  the  power 
of  the  body  to  withstand  the  shock  and  subse- 
quently heal  the  wound. 

With  these  secondary  troubles  no  longer  to 
disturb  him,  the  surgeon  has  become  more  and 
more  bold.  Operations  formerly  not  dreamed  of 
are  now  performed  without  hesitation.  In  former 
years  an  operation  which  opened  the  abdominal 
cavity  was  not  thought  possible,  or  at  least  it  was 
so  nearly  certain  to  result  fatally  that  it  was  re- 
sorted to  only  on  the  last  extremity;  while  to-day 
such  operations  are  hardly  regarded  as  serious. 
Even  brain  surgery  is  becoming  more  and  more 
common.  Possibly  our  surgeons  are  passing  too 
far  to  the  other  extreme,  and,  feeling  their  power  of 
performing  so  many  operations  without  inconven- 
ience or  danger,  they  are  using  the  knife  in  cases 
where  it  would  be  better  to  leave  Nature  to  her- 
self for  her  own  healing.  But,  be  this  as  it  may, 
it  is  impossible  to  estimate  the  amount  of  suffer- 
ing prevented  and  the  number  of  lives  saved  by 
the  mastery  of  the  secondary  inflammatory  trou- 
bles which  used  to  follow  surgical  wounds. 

Preventive  medicine,  then,  has  for  its  object 
the  prevention  rather  than  the  cure  of  disease. 
By  showing  the  causes  of  disease  and  telling  us 
where  and  how  they  are  contracted,  it  is  telling 
us  how  they  may  to  a  large  extent  be  avoided. 
Unlike  practical  medicine,  this  subject  is  one 
which  has  a  direct  relation  to  the  general  public. 


COMBATING   PARASITIC   BACTERIA.  175 

While  it  may  be  best  that  the  knowledge  of  cura- 
tive methods  be  confined  largely  to  the  medical 
profession,  it  is  eminently  desirable  that  a  knowl- 
edge of  all  the  facts  bearing  upon  preventive 
medicine  should  be  distributed  as  widely  as  pos- 
sible. One  person  can  not  satisfactorily  apply 
his  knowledge  of  preventive  medicine  if  his 
neighbour  is  ignorant  of  or  careless  of  the  facts. 
We  can  not  hope  to  achieve  the  possibilities  lying 
along  this  line  until  there  is  a  very  wide  distribu- 
tion of  knowledge.  Every  epidemic  that  sweeps 
through  our  communities  is  a  testimony  to  the 
crying  need  of  education  in  regard  to  such  sim- 
ple facts  as  the  source  of  infectious  material,  the 
methods  of  its  distribution,  and  the  means  of  ren- 
dering it  harmless. 

PREVENTION    IN    INOCULATION. 

It  has  long  been  recognised  that  in  most  cases 
recovery  from  one  attack  of  a  contagious  disease 
renders  an  individual  more  or  less  immune  against 
a  second  attack.  It  is  unusual  for  an  individual 
to  have  the  same  contagious  disease  twice.  This 
belief  is  certainly  based  upon  fact,  although  the 
immunity  thus  acquired  is  subject  to  wide  varia- 
tions. There  are  some  diseases  in  which  there  is 
little  reason  for  thinking  that  any  immunity  is  ac- 
quired, as  in  the  case  of  tuberculosis,  while  there 
are  others  in  which  the  immunity  is  very  great 
and  very  lasting,  as  in  the  case  of  scarlet  fever. 
Moreover,  the  immunity  differs  with  individuals. 
While  some  persons  appear  to  acquire  a  lasting 
immunity  by  recovery  from  a  single  attack,  others 
will  yield  to  a  second  attack  very  readily.  But 
in  spite  of  this  the  fact  of  such  acquired  immu- 

12 


176  THE   STORY  OF   GERM   LIFE. 

nity  is  beyond  question.  Apparently  all  infec- 
tious diseases  from  which  a  real  recovery  takes 
place  are  followed  by  a  certain  amount  of  pro- 
tection from  a  second  attack ;  but  with  some  dis- 
eases the  immunity  is  very  fleeting,  while  with 
others  it  is  more  lasting.  Diseases  which  pro- 
duce a  general  infection  of  the  whole  system  are, 
as  a  rule,  more  likely  to  give  rise  to  a  lasting 
immunity  than  those  which  affect  only  small 
parts.  Tuberculosis,  which,  as  already  noticed, 
is  commonly  quite  localized  in  the  body,  has  lit- 
tle power  of  conveying  immunity,  while  a  disease 
like  scarlet  fever,  which  affects  the  whole  system, 
conveys  a  more  lasting  protection. 

Such  immunity  has  long  been  known,  and  in 
the  earlier  years  was  sometimes  voluntarily  ac- 
quired ;  even  to-day  we  find  some  individuals 
making  use  of  the  principle.  It  appears  that  a 
mild  attack  of  such  diseases  produces  immunity 
equally  well  with  a  severe  attack,  and  acting 
upon  this  fact  mothers  have  not  infrequently 
intentionally  exposed  their  children  to  certain 
diseases  at  seasons  when  they  are  mild,  in  or- 
der to  have  the  disease  "  over  with  "  and  their 
children  protected  in  the  future.  Even  the  more 
severe  diseases  have  at  times  been  thus  vol- 
untarily acquired.  In  China  it  has  sometimes 
been  the  custom  thus  to  acquire  smallpox.  Such 
methods  are  decidedly  heroic,  and  of  course  to  be 
heartily  condemned.  But  the  principle  that  a 
mild  type  of  the  disease  conveys  protection  has 
been  made  use  of  in  a  more  logical  and  defensible 
way. 

The  first  instance  of  this  principle  was  in  vac- 
cination against  smallpox,  now  practised  for  more 
than  a  century.  Cowpox  is  doubtless  closely  re- 


COMBATING   PARASITIC   BACTERIA.  177 

lated  to  smallpox,  and  an  attack  of  the  former 
conveys  a  certain  amount  of  protection  against 
the  latter.  It  was  easy,  therefore,  to  inoculate 
man  with  some  of  the  infectious  material  from 
cowpox,  and  thus  give  him  some  protection 
against  the  more  serious  smallpox.  This  was  a 
purely  empirical  discovery,  and  vaccination  was 
practised  long  before  the  principle  underlying  it 
was  understood,  and  long  before  the  germ  nature 
of  disease  was  recognised.  The  principle  was  re- 
vived again,  however,  by  Pasteur,  and  this  time 
with  a  logical  thought  as  to  its  value.  While 
working  upon  anthrax  among  animals,  he  learned 
that  here,  as  in  other  diseases,  recovery,  when  it 
occurred,  conveyed  immunity.  This  led  him  to 
ask  if  it  were  not  possible  to  devise  a  method  of 
giving  to  animals  a  mild  form  of  the  disease  and 
thus  protect  them  from  the  more  severe  type. 
The  problem  of  giving  a  mild  type  of  this  extraor- 
dinarily severe  disease  was  not  an  easy  one.  It 
could  not  be  done,  of  course,  by  inoculating  the 
animals  with  a  small  number  of  the  bacteria,  for 
their  power  of  multiplication  would  soon  make 
them  indefinitely  numerous.  It  was  necessary 
in  some  way  to  diminish  their  violence.  Pas- 
teur succeeded  in  doing  this  by  causing  them  to 
grow  in  culture  fluids  for  a  time  at  a  high  tem- 
perature. This  treatment  diminished  their  vio- 
lence so  much  that  they  could  be  inoculated  into 
cattle,  where  they  produced  only  the  mildest  type 
of  indisposition,  from  which  the  animals  speedily 
recovered.  But  even  this  mild  type  of  the  dis- 
ease was  triumphantly  demonstrated  to  protect 
the  animals  from  the  most  severe  form  of  an- 
thrax. The  discovery  was  naturally  hailed  as  a 
most  remarkable  one,  and  one  which  promised 


178  THE   STORY   OF   GERM   LIFE. 

great  things  in  the  future.  If  it  was  thus  possi- 
ble, by  direct  laboratory  methods,  to  find  a 
means  of  inoculating  against  a  serious  disease 
like  anthrax,  why  could  not  the  same  principle  be 
applied  to  human  diseases  ?  The  enthusiasts  be- 
gan at  once  to  look  forward  to  a  time  when  all 
diseases  should  be  thus  conquered. 

But  the  principle  has  not  borne  the  fruit  at 
first  expected.  There  is  little  doubt  that  it  might 
be  applied  to  quite  a  number  of  human  diseases 
if  a  serious  attempt  should  be  made.  But  several 
objections  arise  against  its  wide  application.  In  the 
first  place,  the  inoculation  thus  necessary  is  really 
a  serious  matter.  Even  vaccination,  as  is  well 
known,  sometimes,  through  faulty  methods,  re- 
sults fatally,  and  it  is  a  very  serious  thing  to 
experiment  upon  human  beings  with  anything  so 
powerful  for  ill  as  pathogenic  bacteria.  The  seri- 
ousness of  the  disease  smallpox,  its  extraordinary 
contagiousness,  and  the  comparatively  mild  results 
of  vaccination,  have  made  us  willing  to  undergo 
vaccination  at  times  of  epidemics  to  avoid  the 
somewhat  great  probability  of  taking  the  disease. 
But  mankind  is  unwilling  to  undergo  such  an  op- 
eration, even  though  mild,  for  the  purpose  of 
avoiding  other  less  severe  diseases,  or  diseases 
which  are  less  likely  to  be  taken.  We  are  un- 
willing to  be  inoculated  against  mild  diseases, 
or  against  the  more  severe  ones  which  are 
uncommon.  For  instance,  a  method  has  been 
devised  for  rendering  animals  immune  against 
lockjaw,  which  would  probably  apply  equally 
well  to  man.  But  mankind  in  general  will  never 
adopt  it,  since  the  danger  from  lockjaw  is  so 
small.  Inoculation  must  then  be  reserved  for 
diseases  which  are  so  severe  and  so  common,  or 


COMBATING  PARASITIC   BACTERIA.  179 

which  occur  in  periodical  epidemics  of  so  great 
severity,  as  to  make  people  in  general  willing  to 
submit  to  inoculation  as  a  protection.  A  further 
objection  arises  from  the  fact  that  the  immunity 
acquired  is  not  necessarily  lasting.  The  cattle 
inoculated  against  anthrax  retain  their  protective 
powers  for  only  a  few  months.  How  long  similar 
immunity  might  be  retained  in  other  cases  we  can 
not  say,  but  plainly  this  fact  would  effectually 
prevent  this  method  of  protecting  mankind  from 
being  used  except  in  special  cases.  .  It  is  out  of 
the  question  to  think  of  constant  and  repeated 
inoculations  against  various  diseases. 

As  a  result,  the  principle  of  inoculation  as  an 
aid  in  preventive  medicine  has  not  proved  of  very 
much  value.  The  only  other  human  disease  in 
which  it  has  been  attempted  seriously  is  Asiatic 
cholera.  This  disease  in  times  of  epidemics  is  so 
severe  and  the  chance  of  infection  is  so  great  as 
to  justify  such  inoculation.  Several  bacteriolo- 
gists have  in  the  last  few  years  been  trying  to 
discover  a  harmless  method  of  inoculating  against 
this  disease.  Apparently  they  have  succeeded, 
for  experiments  in  India,  the  home  of  the  chol- 
era, have  been  as  successful  as  could  be  antici- 
pated. Bacteriological  science  has  now  in  its 
possession  a  means  of  inoculation  against  chol- 
era which  is  perhaps  as  efficacious  as  vaccination 
is  against  smallpox.  Whether  it  will  ever  be  used 
to  any  extent  is  doubtful,  since,  as  already  pointed 
out,  we  are  in  a  position  to  avoid  cholera  epidemics 
by  other  means.  If  we  can  protect  our  commu- 
nities by  guarding  the  water  supply,  it  is  not 
likely  that  the  method  of  inoculation  will  ever  be 
widely  used. 

Another  instance  of  the  application  of  pre- 


l8o  THE  STORY  OF  GERM   LIFE. 

ventive  inoculation  has  been  made,  but  one  based 
upon  a  different  principle.  Hydrophobia  is  cer- 
tainly one  of  the  most  horrible  of  diseases,  al- 
though comparatively  rare.  Its  rarity  would  ef- 
fectually prevent  mankind  from  submitting  to 
a  general  inoculation  against  it,  but  its  severity 
would  make  one  who  had  been  exposed  to  it 
by  the  bite  of  a  rabid  animal  ready  to  submit 
to  almost  any  treatment  that  promised  to  ward 
off  the  disease.  In  the  attempt  to  dis'cover  a 
means  of  inoculating  against  this  disease  it  was 
necessary,  therefore,  to  find  a  method  that  could 
be  applied  after  the  time  of  exposure — i.  e.,  after 
the  individual  had  been  bitten  by  the  rabid  ani- 
mal. Fortunately,  the  disease  has  a  long  period 
of  incubation,  and  one  that  has  proved  long 
enough  for  the  purpose.  A  method  of  inocula- 
tion against  this  disease  has  been  devised  by  Pas- 
teur, which  can  be  applied  after  the  individual 
has  been  bitten  by  the  rabid  animal.  Apparently, 
however,  this  preventive  inoculation  is  dependent 
upon  a  different  principle  from  vaccination  or  in- 
oculation against  anthrax.  It  does  not  appear  to 
give  rise  to  a  mild  form  of  the  disease,  thus  pro- 
tecting the  individual,  but  rather  to  an  acquired 
tolerance  of  the  chemical  poisons  produced  by 
the  disease.  It  is  a  well-known  physiological  fact 
that  the  body  can  become  accustomed  to  tolerate 
poisons  if  inured  to  them  by  successively  larger 
and  larger  doses.  It  is  by  this  power,  apparently, 
that  the  inoculation  against  hydrophobia  produces 
its  effect.  Material  containing  the  hydrophobia 
poison  (taken  from  the  spinal  cord  of  a  rabbit 
dead  with  the  disease)  is  injected  into  the  indi- 
vidual after  he  has  been  bitten  by  a  rabid  animal. 
The  poisonous  material  in  the  first  injection  is 


COMBATING   PARASITIC   BACTERIA.  181 

very  weak,  but  is  followed  later  by  a  more  powerful 
inoculation.  The  result  is  that  after  a  short  time 
the  individual  has  acquired  the  power  of  resisting 
the  hydrophobia  poisons.  Before  the  incubation 
period  of  the  original  infectious  matter  from  the 
bite  of  the  rabid  animal  has  passed,  the  inoculated 
individual  has  so  thoroughly  acquired  a  tolerance 
of  the  poison  that  he  successfully  resists  the  attack 
of  the  infection.  This  method  of  inoculation  thus 
neutralizes  the  effects  of  the  disease  by  anticipat- 
ing them. 

The  method  of  treatment  of  hydrophobia  met 
with  extraordinarily  violent  opposition.  For  sev- 
eral years  it  was  regarded  as  a  mistake.  But  the 
constantly  accumulating  statistics  from  the  Pas- 
teur Institute  have  been  so  overwhelmingly  on 
one  side  as  to  quiet  opposition  and  bring  about  a 
general  conviction  that  the  method  is  a  success. 

The  method  of  preventive  inoculation  has  not 
been  extensively  applied  to  human  diseases  in  ad- 
dition to  those  mentioned.  In  a  few  cases  a  similar 
method  has  been  used  to  guard  against  diphtheria. 
Among  animals,  experiment  has  shown  that  such 
methods  can  quite  easily  be  obtained,  and  doubt- 
less the  same  would  be  true  of  mankind  if  it  was 
thought  practical  or  feasible  to  apply  them.  But, 
for  reasons  mentioned,  this  feature  of  preventive 
medicine  will  always  remain  rather  unimportant, 
and  will  be  confined  to  a  few  of  the  more  violent 
diseases. 

It  may  be  well  to  raise  the  question  as  to  why 
a  single  attack  with  recovery  conveys  immunity. 
This  question  is  really  a  part  of  the  one  already 
discussed  as  to  the  method  by  which  the  body 
cures  disease.  We  have  seen  that  this  is  in  part 
due  to  the  development  of  chemical  substances 


1 82  THE  STORY  OF  GERM   LIFE. 

which  either  neutralize  the  poisons  or  act  as 
germicide  upon  the  bacteria,  or  both,  and  perhaps 
due  in  part  to  an  active  destruction  of  bacteria 
by  cellular  activity  (phagocytosis).  There  is  little 
reason  to  doubt  that  it  is  the  same  set  of  activi- 
ties which  renders  the  animal  immune.  The  forces 
which  drive  off  the  invading  bacteria  in  one  case 
are  still  present  to  prevent  a  second  attack  of  the 
same  species  of  bacterium.  The  length  of  time 
during  which  these  forces  are  active  and  sufficient 
to  cope  with  any  new  invaders  determines  the 
length  of  time  during  which  the  immunity  lasts. 
Until,  therefore,  we  can  answer  with  more  exact- 
ness just  how  cure  is  brought  about  in  case  of 
disease,  we  shall  be  unable  to  explain  the  method 
of  immunity. 

LIMITS    OF    PREVENTIVE    MEDICINE. 

With  all  the  advance  in  preventive  medicine 
we  can  not  hope  to  avoid  disease  entirely.  We 
are  discovering  that  the  sources  of  disease  are  on 
all  sides  of  us,  and  so  omnipresent  that  to  avoid 
them  completely  is  impossible.  If  we  were  to 
apply  to  our  lives  all  the  safeguards  which  bac- 
teriology has  taught  us  should  be  applied  in  order 
to  avoid  the  different  diseases,  we  would  surround 
ourselves  with  conditions  which  would  make  life 
intolerable.  It  would  be  oppressive  enough  for 
us  to  eat  no  food  except  when  it  is  hot,  to  drink 
no  water  except  when  boiled,  and  to  drink  no 
milk  except  after  sterilization  ;  but  these  would 
not  satisfy  the  necessary  conditions  for  avoiding 
disease.  To  meet  all  dangers,  we  should  handle 
nothing  which  has  not  been  sterilized,  or  should 
follow  the  handling  by  immediately  sterilizing  the 


COMBATING   PARASITIC   BACTERIA.  183 

hands;  we  should  wear  only  disinfected  clothes; 
we  should  never  put  our  fingers  in  our  mouths 
or  touch  our  food  with  them  ;  we  should  cease 
to  ride  in  public  conveyances,  and,  indeed, 
should  -cease  to  breathe  common  air.  Absolute 
prevention  of  the  chance  of  infection  is  impos- 
sible. The  most  that  preventive  medicine  can 
hope  for  is  to  point  out  the  most  common  and 
prolific  sources  of  infection,  and  thus  enable 
civilized  man  to  avoid  some  of  his  most  common 
troubles.  It  becomes  a  question,  therefore,  where 
we  will  best  draw  the  line  in  the  employment  of 
safeguards.  Shall  we  drink  none  except  sterilized 
milk,  and  no  water  unless  boiled  ?  or  shall  we  put 
these  occasional  sources  of  danger  in  the  same 
category  with  bicycle  and  railroad  accidents,  dan- 
gers which  can  be  avoided  by  not  using  the  bicycle 
or  riding  on  the  rail,  but  in  regard  to  which  the 
remedy  is  too  oppressive  for  application  ? 

Indeed,  when  viewed  in  a  broad  philosophical 
light  it  may  not  be  the  best  course  for  mankind 
to  shun  all  dangers.  Strength  in  the  organism 
comes  from  the  use  rather  than  the  disuse  of  our 
powers.  It  is  certain  that  the  general  health  and 
vigour  of  mankind  is  to  be  developed  by  meeting 
rather  than  by  shunning  dangers.  Resistance  to 
disease  means  bodily  vigour,  and  this  is  to  be  de- 
veloped in  mankind  by  the  application  of  the 
principle  of  natural  selection.  In  accordance 
with  this  principle,  disease  will  gradually  remove 
the  individuals  of  weak  resisting  powers,  leaving 
those  of  greater  vigour.  Parasitic  bacteria  are 
thus  a  means  of  preventing  the  continued  life  of 
the  weaker  members  of  the  community,  and  so 
tend  to  strengthen  mankind.  By  preventive  med- 
icine many  a  weak  individual  who  would  other- 


184  THE   STORY  OF  GERM   LIFE. 

wise  succumb  earlier  in  the  struggle  is  enabled  to 
live  a  few  years  longer.  Whatever  be  our  humani- 
tarian feeling  for  the  individual,  we  can  not  fail 
to  admit  that  this  survival  of  the  weak  is  of  no 
benefit  to  the  race  so  far  as  the  development  of 
physical  nature  is  concerned.  Indeed,  if  we  were 
to  take  into  consideration  simply  the  physical 
nature  of  man  we  should  be  obliged  to  recom- 
mend a  system  such  as  the  ancient  Spartans  de- 
veloped, of  exposing  to  death  all  weakly  individ- 
uals, that  only  the  strong  might  live  to  become 
the  fathers  of  future  generations.  In  this  light, 
of  course,  parasitic  diseases  would  be  an  assist- 
ance rather  than  a  detriment  to  the  human  race. 
Of  course  such  principles  will  never  again  be 
dominant  among  men,  and  our  conscience  tells  us 
to  do  all  we  can  to  help  the  weak.  We  shall 
doubtless  do  all  possible  to  develop  preventive 
medicine  in  order  to  guard  the  weak  against  para- 
sitic organisms.  But  it  is  at  all  events  well  for  us 
to  remember  that  we  can  never  hope  to  develop  the 
strength  of  the  human  race  by  shunning  evil,  but 
rather  by  combating  it,  and  the  power  of  the 
human  race  to  resist  the  invasions  of  these  or- 
ganisms will  never  be  developed  by  the  line  of 
action  which  guards  us  from  attack.  Here,  as  in 
other  directions,  the  principles  of  modern  humanity 
have,  together  with  their  undoubted  favourable 
influence  upon  mankind,  certain  tendencies  toward 
weakness.  While  we  shall  still  do  our  utmost  to 
develop  preventive  medicine  in  a  proper  way,  it 
may  be  well  for  us  to  remember  these  facts  when 
we  come  to  the  practical  question  of  determining 
where  to  draw  the  limits  of  the  application  of 
methods  for  preventing  infectious  diseases. 


COMBATING   PARASITIC   BACTERIA.  185 

CURATIVE    MEDICINE. 

Bacteriology  has  hitherto  contributed  less  to 
curative  than  to  preventive  medicine.  Neverthe- 
less, its  contributions  to  curative  medicine  have 
not  been  unimportant,  and  there  is  promise  of 
much  more  in  the  future.  It  is,  of  course,  unsafe 
to  make  predictions  for  the  future,  but  the  accom- 
plishments of  the  last  few  years  give  much  hope 
as  to  further  results. 


DRUGS. 

It  was  at  first  thought  that  a  knowledge  of 
the  specific  bacteria  which  cause  a  disease  would 
give  a  ready  means  of  finding  specific  drugs  for 
the  cure  of  such  disease.  If  a  definite  species  of 
bacterium  causes  a  disease  and  we  can  cultivate 
the  organism  in  the  laboratory,  it  is  easy  to  find 
some  drugs  which  will  be  fatal  to  its  growth,  and 
these  same  drugs,  it  would  seem,  should  be  valu- 
able as  medicines  in  these  diseases.  This  hope 
has,  however,  proved  largely  illusive.  It  is  very 
easy  to  find  some  drug  which  proves  fatal  to  the 
specific  germs  while  growing  in  the  culture  media 
of  the  laboratory,  but  commonly  these  are  of  little 
or  no  use  when  applied  as  medicines.  In  the  first 
place,  such  substances  are  usually  very  deadly  poi- 
sons. Corrosive  sublimate  is  a  substance  which 
destroys  all  pathogenic  germs  with  great  rapidity, 
but  it  is  a  deadly  poison,  and  can  not  be  used  as  a 
drug  in  sufficient  quantity  to  destroy  the  parasitic 
bacteria  in  the  'body  without  at  the  same  time 
producing  poisonous  effects  on  the  body  itself. 
It  is  evident  that  for  any  drug  to  be  of  value  in 
thus  destroying  bacteria  it  must  have  some  spe- 


1 86  THE   STORY  OF   GERM   LIFE. 

cially  strong  action  upon  the  bacteria.  Its  germi- 
cide action  on  the  bacteria  should  be  so  strong 
that  a  dose  which  would  be  fatal  or  very  injurious 
to  them  would  be  too  small  to  have  a  deleterious 
influence  on  the  body  of  the  individual.  It  has 
not  proved  an  easy  task  to  discover  drugs  which 
will  have  any  value  as  germicides  when  used  in 
quantities  so  small  as  to  produce  no  injurious 
effect  on  the  body. 

A  second  difficulty  is  in  getting  the  drug  to 
produce  its  effect  at  the  right  point.  A  few 
diseases,  as  we  have  noticed,  'are  produced  by 
bacteria  which  distribute  themselves  almost 
indiscriminately  over  the  body  ;  but  the  majority 
are  somewhat  definitely  localized  in  special 
points.  Tuberculosis  may  attack  a  single  gland 
or  a  single  lobe  of  the  lung.  Typhoid  germ  is 
localized  in  the  intestines,  liver,  spleen,  etc. 
Even  if  it  were  possible  to  find  some  drug  which 
would  have  a  very  specific  effect  upon  the  tuber- 
culosis bacillus,  it  is  plain  that  it  would  be  a  very 
questionable  method  of  procedure  to  introduce 
this  into  the  whole  system  simply  that  it  might 
have  an  effect  upon  a  very  small  isolated  gland. 
Sometimes  such  a  bacterial  affection  may  be  local- 
ized in  places  where  it  can  be  specially  treated,  as 
in  the  case  of  an  attack  on  a  dermal  gland,  and  in 
these  cases  some  of  the  germicides  have  proved  to 
be  of  much  value.  Indeed,  the  use  of  various  dis- 
infectants connected  with  abscesses  and  super- 
ficial infections  has  proved  of  much  value.  To 
this  extent,  in  disinfecting  wounds  and  as  a  local 
application,  the  development  of  our  knowledge 
of  disinfectants  has  given  no  little  aid  to  curative 
medicine. 

Very  little  success,  however,  has  resulted  in  the 


COMBATING   PARASITIC   BACTERIA.  187 

attempt  to  find  specific  drugs  for  specific  diseases, 
and  it  is  at  least  doubtful  whether  many  such  will 
ever  be  found.  The  nearest  approach  to  it  is  qui- 
nine as  a  specific  poison  for  malarial  troubles. 
Malarious  diseases  are  not,  however,  produced  by 
bacteria  but  by  a  microscopic  organism  of  a  very 
different  nature,  thought  to  be  an  animal  rather 
than  a  plant.  Besides  this  there  has  been  little 
or  no  success  in  discovering  specifics  in  the  form 
of  drugs  which  can  be  given  as  medicines  or  inocu- 
lated with  the  hope  of  destroying  special  kinds  of 
pathogenic  bacteria  without  injury  to  the  body. 
While  it  is  unwise  to  make  predictions  as  to  future 
discoveries,  there  seems  at  present  little  hope  for 
a  development  of  curative  medicine  along  these 
lines. 

VIS    MEDICATRIX    NATURE. 

The  study  of  bacterial  diseases  as  they  pro- 
gress in  the  body  has  emphasized  above  all  things 
the  fact  that  diseases  are  eventually  cured  by  a 
natural  rather  than  by  an  artificial  process.  If  a 
pathogenic  bacterium  succeeds  in  passing  the 
outer  safeguards  and  entering  the  body,  and  if  it 
then  succeeds  in  overcoming  the  forces  of  resist- 
ance which  we  have  already  noticed,  it  will  begin 
to  multiply  and  produce  mischief.  This  multi- 
plication now  goes  on  for  a  time  unchecked,  and 
there  is  little  reason  to  expect  that  we  can  ever 
do  much  toward  checking  it  by  means  of  drugs. 
But  after  a  little,  conditions  arise  which  are  hos- 
tile to  the  further  growth  of  the  parasite.  These 
hostile  conditions  are  produced  perhaps  in  part 
by  the  secretions  from  the  bacteria,  for  bacteria 
are  unable  to  flourish  in  a  medium  containing 
much  of  their  own  secretions.  The  secretions 


1 88  THE   STORY  OF  GERM   LIFE. 

which  they  produce  are  poisons  to  them  as  well 
as  to  the  individual  in  which  they  grow,  and 
after  these  have  become  quite  abundant  the  fur- 
ther growth  of  the  bacterium  is  checked  and 
finally  stopped.  Partly,  also,  must  we  conclude 
that  these  hostile  conditions  are  produced  by 
active  vital  powers  in  the  body  of  the  individual 
attacked.  The  individual,  as  we  have  seen,  in 
some  cases  develops  a  quantity  of  some  substance 
which  neutralizes  the  bacterial  poisons  and  thus 
prevents  their  having  their  maximum  effect.  Thus 
relieved  from  the  direct  effects  of  the  poisons,  the 
resisting  powers  are  recuperated  and  once  more 
begin  to  produce  a  direct  destruction  of  the  bac- 
teria. Possibly  the  bacteria,  being  now  weakened 
by  the  presence  of  their  own  products  of  growth, 
more  readily  yield  to  the  resisting  forces  of  the 
cell  life  of  the  body.  Possibly  the  resisting  forces 
are  decidedly  increased  by  the  reactive  effect  of 
the  bacteria  and  their  poisons.  But,  at  all  events, 
in  cases  where  recovery  from  parasitic  diseases 
occurs,  the  revived  powers  of  resistance  finally 
overcome  the  bacteria,  destroy  them  or  drive 
them  off,  and  the  body  recovers. 

All  this  is,  of  course,  a  natural  process.  The 
recovery  from  a  disease  produced  by  the  invasion 
of  parasitic  bacteria  depends  upon  whether  the 
body  can  resist  the  bacterial  poisons  long  enough 
for  the  recuperation  of  its  resisting  powers.  If 
these  poisons  are  very  violent  and  produced  rap- 
idly, death  will  probably  occur  before  the  resisting 
powers  are  strong  enough  to  drive  off  the  bacteria. 
In  the  case  of  some  diseases  the  poisons  are  so 
violent  that  this  practically  always  occurs,  recov- 
ery being  very  exceptional.  The  poison  produced 
by  the  tetanus  bacillus  is  of  this  nature,  and  recov- 


COMBATING   PARASITIC   BACTERIA.  189 

ery  from  lockjaw  is  of  the  rarest  occurrence.  But 
in  many  other  diseases  the  body  is  able  to  with- 
stand the  poison,  and  later  to  recover  its  resisting 
powers  sufficiently  to  drive  off  the  invaders.  In 
all  cases,  however,  the  process  is  a  natural  one  and 
dependent  upon  the  vital  activity  of  the  body.  It 
is  based  at  the  foundation,  doubtless,  upon  the 
powers  of  the  body  cells,  either  the  phagocytes 
or  other  active  cells.  The  body  has,  in  short,  its 
own  forces  for  repelling  invasions,  and  upon  these 
forces  must  we  depend  for  the  power  to  produce 
recovery. 

It  is  evident  that  all  these  facts  give  us  very 
little  encouragement  that  we  shall  ever  be  able 
to  cure  diseases  directly  by  means  of  drugs  to 
destroy  bacteria,  but,  on  the  contrary,  that  we 
must  ever  depend  upon  the  resisting  powers  of 
the  body.  They  teach  us,  moreover,  along  what 
line  we  must  look  for  the  future  development 
of  curative  medicine.  It  is  evident  that  scien- 
tific medicine  must  turn  its  attention  toward 
the  strengthening  and  stimulating  of  the  resist- 
ing and  curative  forces  of  the  body.  It  must 
be  the  physician's  aim  to  enable  the  body  to  re- 
sist the  poisons  as  well  as  possible  and  to  stimu- 
late it  to  re-enforce  its  resistant  forces.  Drugs 
have  a  place  in  medicine,  of  course,  but  this  place 
is  chiefly  to  stimulate  the  body  to  react  against 
its  invading  hosts.  They  are,  as  a  rule,  not  spe- 
cific against  definite  diseases.  We  can  not  hope 
for  much  in  the  way  of  discovering  special  medi- 
cines adapted  to  special  diseases.  -We  must  sim- 
ply look  upon  them  as  means  which  the  physician 
has  in  hand  for  stimulating  the  natural  forces  of 
the  body,  and  these  may  doubtless  vary  with  dif- 
ferent individual  natures.  Recognising  this,  we 


190  THE   STORY   OF   GERM   LIFE. 

can  see  also  the  logic  of  the  small  dose  as  com- 
pared to  the  large  dose.  A  small  dose  of  a 
drug  may  serve  as  a  stimulant  for  the  lagging 
forces,  while  a  larger  dose  would  directly  repress 
them  or  produce  injurious  secondary  effects.  As 
soon  as  we  recognise  that  the  aim  of  medicine  is 
not  to  destroy  the  disease  but  rather  to  stimulate 
the  resisting  forces  of  the  body,  the  whole  logic 
of  therapeutics  assumes  a  new  aspect. 

Physicians  have  understood  this,  and,  espe- 
cially in  recent  years,  have  guided  their  practice 
by  it.  If  a  moderate  dose  of  quinine  will  check 
malaria  in  a  few  days,  it  does  not  follow  that 
twice  the  dose  will  do  it  in  half  the  time  or  with 
twice  the  certainty.  The  larger  doses  of  the 
past,  intended  to  drive  out  the  disease,  have  been 
everywhere  replaced  by  smaller  doses  designed 
to  stimulate  the  lagging  body  powers.  The  mod- 
ern physician  makes  no  attempt  to  cure  typhoid 
fever,  having  long  since  learned  his  inability  to 
do  this,  at  least  if  the  fever  once  gets  a  foothold  ; 
but  he  turns  his  attention  to  every  conceivable 
means  of  increasing  the  body's  strength  to  resist 
the  typhoid  poison,  confident  that  if  he  can  thus 
enable  the  patient  to  resist  the  poisoning  effects 
of  the  typhotoxine  his  patient  will  in  the  end  re- 
act against  the  disease  and  drive  off  the  invading 
bacteria.  The  physician's  duty  is  to  watch  and 
guard,  but  he  must  depend  upon  the  vital  powers 
of  his  patient  to  carry  on  alone  the  actual  battle 
with  the  bacterial  invaders. 


ANTITOXINES. 

In  very  recent  times,  however,  our  bacteriolo- 
gists have  been  pointing  out  to  the  world  certain 


COMBATING   PARASITIC   BACTERIA.  191 

entirely  new  means  of  assisting  the  body  to  fight 
its  battles  with  bacterial  diseases.  As  already 
noticed,  one  of  the  primal  forces  in  the  recovery, 
from  some  diseases,  at  least,  is  the  development 
in  the  body  of  a  substance  which  acts  as  an  anti- 
dote to  the  bacterial  poison.  So  long  as  this  anti- 
toxine  is  not  present  the  poisons  produced  by  the 
disease  will  have  their  full  effect  to  weaken  the 
body  and  prevent  the  revival  of  its  resisting 
powers  to  drive  off  the  bacteria.  Plainly,  if  it  is 
possible  to  obtain  this  antitoxine  in  quantity  and 
then  inoculate  it  into  the  body  when  the  toxic 
poisons  are  present,  we  have  a  means  for  de- 
cidedly assisting  the  body  in  its  efforts  to  drive 
off  the  parasites.  Such  an  antidote  to  the  bac- 
terial poison  would  not,  indeed,  produce  a  cure, 
but  it  would  perhaps  have  the  effect  of  annulling 
the  action  of  the  poisons,  and  would  thus  give  the 
body  a  much  greater  chance  to  master  the  bac- 
teria. It  is  upon  this  principle  that  is  based  the 
use  of  antitoxines  in  diphtheria  and  tetanus. 

It  will  be  clear  that  to  obtain  the  antitoxine 
we  must  depend  upon  some  natural  method  for 
its  production.  We  do  not  know  enough  of  the 
chemical  nature  of  the  antitoxines  to  manufacture 
them  artificially.  Of  course  we  can  not  deny  the 
possibility  of  their  artificial  production,  and  cer- 
tain very  recent  experiments  indicate  that  per- 
haps they  may  be  made  by  the  agency  of  elec- 
tricity. At  present,  however,  we  must  use  natural 
methods,  and  the  one  commonly  adopted  is  sim- 
ple. Some  animal  is  selected  whose  blood  is 
harmless  to  man  and  that  is  subject  to  the  dis- 
ease to  be  treated.  For  diphtheria  a  horse  is 
chosen.  This  animal  is  inoculated  with  small 
quantities  of  the  diphtheria  poison  without  the 


192  THE   STORY   OF   GERM   LIFE. 

diphtheria  bacillus.  This  poison  is  easily  ob- 
tained by  causing  the  diphtheria  bacillus  to  grow 
in  common  media  in  the  laboratory  for  a  while, 
and  the  toxines  develop  in  quantity  ;  then,  by 
proper  filtration,  the  bacteria  themselves  can  be 
removed,  leaving  a  pure  solution  of  the  toxic 
poison.  Small  quantities  of  this  poison  are  inocu- 
lated into  the  horse  at  successive  intervals.  The 
effect  on  the  horse  is  the  same  as  if  the  animal 
had  the  disease.  Its  cells  react  and  produce  a 
considerable  quantity  of  the  antitoxine  which 
remains  in  solution  in  the  blood  of  the  animal. 
This  is  not  theory,  but  demonstrated  fact.  The 
blood  of  a  horse  so  treated  is  found  to  have  the 
effect  of  neutralizing  the  diphtheria  poison,  al- 
though the  blood  of  the  horse  before  such  treat- 
ment has  no  such  effect.  Thus  there  is  developed 
in  the  horse's  blood  a  quantity  of  the  antitoxine, 
and  now  it  may  be  used  by  physicians  where 
needed.  If  some  of  this  horse's  blood,  properly 
treated,  be  inoculated  into  the  body  of  a  person 
who  is  suffering  from  diphtheria,  its  effect,  pro- 
vided the  theory  of  antitoxines  is  true,  will  be  to 
counteract  in  part,  at  least,  the  poisons  which  are 
being  produced  in  the  patient  by  the  diphtheria 
bacillus.  This  does  not  cure  the  disease  nor  in 
itself  drive  off  the  bacilli,  but  it  does  protect  the 
body  from  the  poisons  to  such  an  extent  as  to 
enable  it  more  readily  to  assert  its  own  resisting 
powers. 

This  method  of  using  antitoxines  as  a  help  in 
curing  disease  is  very  recent,  and  we  can  not  even 
guess  what  may  come  of  it.  It  has  apparently 
been  successfully  applied  in  diphtheria.  It  has 
also  been  used  in  tetanus  with  slight  success. 
The  same  principle  has  been  used  in  obtaining  an 


COMBATING   PARASITIC   BACTERIA.         '    193 

antidote  for  the  poison  of  snake  bites,  since  it  has 
appeared  that  in  this  kind  of  poisoning  the  body 
will  develop  an  antidote  to  the  poison  if  it  gets  a 
chance.  Horses  have  been  treated  in  the  same 
way  as  with  the  diphtheria  poison,  and  in  the 
same  way  they  develop  a  substance  which  neu- 
tralizes the  snake  poison.  Other  diseases  are 
being  studied  to-day  with  the  hope  of  similar 
results.  How  much  further  the  principle  will  go 
we  can  not  say,  nor  can  we  be  very  confident  that 
the  same  principle  will  apply  very  widely.  The 
parasitic  diseases  are  so  different  in  nature  that 
we  can  hardly  expect  that  a  method  which  is  satis- 
factory in  meeting  one  of  the  diseases  will  be  very 
likely  to  be  adapted  to  another.  Vaccination  has 
proved  of  value  in  smallpox,  but  is  not  of  use  in 
other  human  diseases.  Inoculation  with  weak- 
ened germs  has  proved  of  value  in  anthrax  and 
fowl  cholera,  but  will  not  apply  to  all  diseases. 
Each  of  these  parasites  must  be  fought  by  special 
methods,  and  we  must  not  expect  that  a  method 
that  is  of  value  in  one  case  must  necessarily  be 
of  use  elsewhere.  Above  all,  we  must  remember 
that  the  antitoxines  do  not  cure  in  themselves; 
they  only  guard  the  body  from  the  weakening 
effects  of  the  poisons  until  it  can  cure  itself,  and, 
unless  the  body  has  resisting  powers,  the  anti- 
toxine  will  fail  to  produce  the  desired  results. 

One  further  point  in  the  action  of  the  anti- 
toxines must  be  noticed.  As  we  have  seen,  a 
recovery  from  an  attack  of  most  germ  diseases 
renders  the  individual  for  a  time  immune  against 
a  second  attack.  This  applies  less,  however,  to  a 
recovery  after  the  artificial  inoculation  with  anti- 
toxine  than  when  the  individual  recovers  without 
such  aid.  If  the  individual  recovers  quite  inde- 


194  THE   STORY  OF  GERM   LIFE. 

pendently  of  the  artificial  antitoxine,  he  does  so 
in  part  because  he  has  developed  the  antitoxines 
for  counteracting  the  poison  by  his  own  powers. 
His  cellular  activities  have,  in  other  words,  been 
for  a  moment  at  least  turned  in  the  direction  of 
production  of  antitoxines.  It  is  to  be  expected, 
therefore,  that  after  the  recovery  they  will  still 
have  this  power,  and  so  long  as  they  possess  it 
the  individual  will  have  protection  from  a  second 
attack.  When,  however,  the  recovery  results  from 
•the  artificial  inoculation  of  antitoxine  the  body 
cells  have  not  actively  produced  antitoxine.  The 
neutralization  of  the  poisons  has  been  a  passive 
one,  and  after  recovery  the  body  cells  are  no 
more  engaged  in  producing  antitoxine  than  be- 
fore. The  antitoxine  which  was  inoculated  is 
soon  eliminated  by  secretion,  and  the  body  is 
left  with  practically  the  same  liability  to  attack 
as  before.  Its  immunity  is  decidedly  fleeting, 
since  it  was  dependent  not  upon  any  activity  on 
the  part  of  the  body,  but  upon  an  artificial  inocu- 
lation of  a  material  which  is  rapidly  eliminated 
by  secretion. 

CONCLUSION. 

It  is  hoped  that  the  outline  which  has  been 
given  of  the  bacterial  life  of  Nature  may  serve  to 
give  some  adequate  idea  of  these  organisms  and 
correct  the  erroneous  impressions  in  regard  to 
them  which  are  widely  prevalent.  It  will  be  seen 
that,  as  our  friends,  bacteria  play  a  vastly  more 
important  part  in  Nature  than  they  do  as  our 
enemies.  These  plants  are  minute  and  extraor- 
dinarily simple,  but,  nevertheless,  there  exists  a 
large  number  of  different  species.  The  number 


COMBATING  PARASITIC   BACTERIA.  195 

of  described  forms  already  runs  far  into  the  hun- 
dreds, and  we  do  not  yet  appear  to  be  approach- 
ing the  end  of  them.  They  are  everywhere  in 
Nature,  and  their  numbers  are  vast  beyond  con- 
ception. Their  powers  of  multiplication  are  in- 
conceivable, and  their  ability  to  produce  profound 
chemical  changes  is  therefore  unlimited.  This 
vast  host  of  living  beings  thus  constitutes  a  force 
or  series  of  forces  of  tremendous  significance. 
Most  of  the  vast  multitude  we  must  regard  as 
our  friends.  Upon  them  the  farmer  is  dependent 
for  the  fertility  of  his  soil  and  the  possibility  of 
continued  life  in  his  crops.  Upon  them  the 
dairyman  is  dependent  for  his  flavours.  Upon 
them  important  fermentative  industries  are  de- 
pendent, and  their  universal  powers  come  into 
action  upon  a  commercial  scale  in  many  a  place 
where  we  have  little  thought  of  them  in  past 
years.  We  must  look  upon  them  as  agents  ever 
at  work,  by  means  of  which  the  surface  of  Nature 
is  enabled  to  remain  fresh  and  green.  Their 
power  is  fundamental,  and  their  activities  are 
necessary  for  the  continuance  of  life.  A  small 
number  of  the  vast  host,  a  score  or  two  of  spe- 
cies, unfortunately  for  us,  find  their  most  favour- 
able living  place  in  the  human  body,  and  thus 
become  human  parasites.  By  their  growth  they 
develop  poisons  and  produce  disease.  This  small 
class  of  parasites  are  then  decidedly  our  enemies. 
But,  taken  all  together,  we  must  regard  the  bac- 
teria as  friends  and  allies.  Without  them  we 
should  not  have  our  epidemics,  but  without  them 
we  should  not  exist.  Without  them  it  might  be 
that  some  individuals  would  live  a  little  longer,  if 
indeed  we  could  live  at  all.  It  is  true  that  bac- 
teria, by  producing  disease,  once  in  a  while  cause 


196  THE  STORY  OF  GERM   LIFE. 

the  premature  death  of  an  individual ;  once  in  a 
while,  indeed,  they  may  sweep  off  a  hundred  or  a 
thousand  individuals;  but  it  is  equally  true  that 
without  them  plant  and  animal  life  would  be  im- 
possible on  the  face  of  the  earth. 


INDEX. 


A. 

Acetic  acid,  51. 
Alcohol,  48. 
Alexines,  149. 
Amoeba  coll,  165. 
Animals  or  plants  ?  31. 
Anthrax,  137,  177. 
Antitoxines,  157,  190. 
Aroma  of  butter,  76. 

B. 

Bacillus  acidi  lactici,  71. 
Bacillus,  definition  of,  33. 
Bacteria,  defined  by  Hoffman,  15. 
Beer,  bacteria  in   the  manufacture 

of,  50. 

Blood  poisoning,  138,  140. 
Blue  milk,  72. 

study  of,  by  Fuchs,  12. 

Bitter  milk,  72. 
Butter  making,  75,  78. 
Butyric  acid,  56. 

C. 

Canning  industry,  64.  ^ 
Capsule  around  bacteria,  24. 
Cheese   ripening,   86 ;    bacteria   in, 

90. 

Cholera  Asiatica,  135. 
Cholera,  fowl,  144. 
Cholera  infantum,  133. 
Classification  of  bacteria,  33,  36. 
Cleavage  products,  41. 
Coal,  relation  of  bacteria  to,  123. 
Cocoanut  fibre,  44. 
Colony  of  bacteria,  25. 
Compost  heap,  118. 
Cream  ripening,  75,  77. 


Curative  medicine,  185. 
Cure  of  disease  by  natural  processes, 
187. 

D. 

Dairy  industry,  66. 
Decomposition  products,  41. 
Diphtheria,  134. 

Disease,  method  of  production,  130. 
Diseases  produced  by  bacteria,  139, 

142. 

Distribution  of  disease  germs,  168. 
Division  of  bacteria,  method  of,  18, 

20. 

rapidity  of,  21. 

Drugs  in  germ  diseases,  185. 
Dysentery,  165. 

F. 

Farmer's  life,  relation  to  bacteria, 

121. 

Fermentative  industries,  48. 
Fermentation,  theory  of  Liebig,  13. 
Fertilizers,  ripening  of,  117. 
Flagella,  29. 
Flavour  of  butter,  76  ;    of  cheese, 

88. 

Food  cycle  of  Nature,  97. 
Food,  relation  of  bacteria  to,  22. 

G. 

Generic  names,  37. 
Green  manuring,  120. 

H. 

Habitat  of  bacteria,  38. 

Hemp,  44. 

Henle,  general  theory  of  disease,  12. 

Hydrophobia,  180. 


198 


INDEX. 


I. 

Indigo,  preparation  of,  57. 
Inflammation  in  surgery,  153. 
Internal  structure  of  bacteria,  30. 
Invasion,  means  of,  145,  169. 


Jute,  44. 


J. 


K. 


Koch,  contribution  to  bacteriology, 
16. 


Lactic  acid,  55. 

Leather,  46. 

Leeuwenhoek,  studies  of,  ^10. 

Legumes  in  nitrogen  fixation,  108. 

Liebig,  theory  of  fermentation,  13. 

Limits  of  preventive  medicine,  182. 

Linen,  42. 

Lockjaw,  135. 

Lysines,  151. 

M. 

Maceration  industries,  42. 
Maceration  of  skeletons,  46. 
Malaria,  160. 
Malignant  pustule,  137. 
Microbe,  definition  of,  9. 
Micrococcus,  defined,  18. 
Milk  bacteria,  67,  70. 
Milk,  effect  of  bacteria  on,  70. 
Milk  handling,  74. 
Mosquitoes  and  malaria,  164. 
Motion  of  bacteria,  28. 
Miiller,  studies  of,  n. 
Multiplication,  rapidity  of,  21. 
Mycoderma  aceti,  52. 

N. 

Nitrate  beds,  116. 
Nitrifying  bacteria,  103. 
Nitrogen  fixation,  107. 
Nitrogen  loss,  104. 

O. 

Opium,  63. 

Oscillariae,  as  allies  of  bacteria,  32. 

P. 

Parasitic  bacteria,  134. 
Pasteur,  contributions  of,  14. 


Pathogenic  bacteria,  abundance  of, 
129. 

Pathogenic  bacteria  not  true  para- 
sites, 131. 

Phagocytes,  151. 

Poisons  produced  by  bacteria,  130, 
132. 

Preventive  inoculation,  175. 

Preventive  medicine,  166  ;  limits  of, 
182. 

Products  of  bacterial  life,  41,  47. 

Pure  cultures,  15  ;  in  vinegar  mak- 
ingi  51  ;  in  tobacco  curing,  61  ;  in 
butter  making,  82  ;  in  cheese  mak- 

_  ing,  93- 

Pus,  153  ;  pus  cocci,  142. 

R. 

Recovery  from  germ  diseases,  156. 
Red  milk,  72. 
Resistance  to  disease,  147. 

S. 

Sarcina,  defined,  19. 

Sauer  Kraut,  65. 

Scavengers,  bacteria  as,  95,  101. 

Schwann,  studies  on  fermentation, 

12. 

Seeds,  sprouting  of,  in. 
Shape  of  bacteria,  17. 
Silo,  bacteria  in,  112. 
Size  of  bacteria,  17. 
Skeletons,  46. 
Slimy  milk,  72. 
Snuff,  preparation  of,  59. 
Soapy  milk,  72. 
Soil,  fertility  of,  114. 
Sources  of  infectious  material,  168. 
Souring  of  milk,  70. 
Species,  differences  between,  23,  34 ; 

names  of,  37. 
Sponges,  45. 
Spores,  25. 

Staphylococcus  pyogenes,  142. 
Streptococcus,  defined,  19. 
Streptococcus  pyogenes,  142. 
Surgery,  bacteria  in,  171. 
Susceptibility  of  the  individual,  145. 

T. 

Tainted  milk,  72. 

Tetanus,  135. 

Tobacco  curing,  58. 

Troublesome  fermentations,  63, 121. 

Tuberculosis,  136. 

Typhoid  fever,  136. 


INDEX. 


I99 


V. 

Vaccination,  176 

Variation  among  bacteria,  35. 

Vinegar,  51. 

Virulence  of  pathogenic  germs,  140, 

143- 
Vis  medicatrix  naturae,  187. 


W. 

Wine,  bacteria  in  manufacture  of, 
Y. 


Yellow  milk,  72. 
Zoogloea,  24. 


Z. 


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